Oldtimer question (valves/tubes)

[Cursitor Doom]

Gentlemen,

I've got this RF sig gen I'm testing at the moment. It was made in 1955
and is all valve (I say "all valve" but there are only two tubes in it
and only one of those generates the RF - the other's 400Hz for the
modulation).
Anyway, it has 8 ranges in total covering 100KHz to 240Mhz. The
oscillator tube is a double triode, a 12AT7. One half handles range from
100Khz to 30Mhz and the other takes care of 30 - 240Mhz. Now, it all
works great EXCEPT for one range (the 3rd lowest) which has appreciable
distortion present on the output. It looks a bit like it's being over-
driven on my scope. My question is, does a valve like a 12AT7 require
different DC biasing points for every range of frequencies? Obviously the
range switch is switching in different combinations of coils and
capacitors, but is it likely to be also switching in different cathode-
grid DC biasing at the same time?

TIA



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[Fox's Mercantile]

On 5/12/19 6:04 AM, Cursitor Doom wrote:
> My question is, does a valve like a 12AT7 require
> different DC biasing points for every range of frequencies? Obviously the
> range switch is switching in different combinations of coils and
> capacitors, but is it likely to be also switching in different cathode-
> grid DC biasing at the same time?

A make and model would help considerably.
But, I'm gonna generalize here, if it's cheap enough to only
have two tubes, they certainly didn't waste any money on
complications like switchable bias.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

[peterw...@gmail.com]

Keep in mind that a 2-tube SG is, was and ever will be a hobby device. With that in mind, a little, even a lot of distortion which is still "on frequency" hardly matters to a hobbyist aligning a consumer grade radio.

Peter Wieck
Melrose Park, PA

[Cursitor Doom]

On Sun, 12 May 2019 11:04:06 +0000, Cursitor Doom wrote:

[...]

Sorry, guys, it's a Taylor 68A/M. I can't find the exact model on line
but this one is as close as it gets:

https://www.radiomuseum.org/r/taylor_afrf_signal_generator_68a_2.html

The grid/Cathode bias does change with range selection; I just measured
it. There doesn't seem anything obviously amiss with the readings:

Range 8 (lowest frequency) -25V
7: -7V
6: -3.4V
5: -1V
4: -0.3V
3: -1.6V
2: -1.8V
1: -1.0

Anode is +80 to +90VDC vs. Cathode over all ranges.

[John Robertson]

On 2019/05/12 6:05 a.m., Cursitor Doom wrote:
> On Sun, 12 May 2019 11:04:06 +0000, Cursitor Doom wrote:
>
> [...]
>
> Sorry, guys, it's a Taylor 68A/M. I can't find the exact model on line
> but this one is as close as it gets:
>
> https://www.radiomuseum.org/r/taylor_afrf_signal_generator_68a_2.html
>
> The grid/Cathode bias does change with range selection; I just measured
> it. There doesn't seem anything obviously amiss with the readings:
>
> Range 8 (lowest frequency) -25V
> 7: -7V
> 6: -3.4V
> 5: -1V
> 4: -0.3V
> 3: -1.6V
> 2: -1.8V
> 1: -1.0
>
> Anode is +80 to +90VDC vs. Cathode over all ranges.
>
>
>
>

If you are troubleshooting this then be aware that plate resistors often
fail high and are (after capacitors) the next suspects in repairing old
tube/valve equipment. Schematics are a huge help of course to be able to
verify meeting manufacturers BOM as older parts colours have usually
faded to obscurity....antique radio societies will be an aid in tracking
down schematics...

If you can't find a match check out EICO or Heathkit of the same vintage
as chances are someone may have copied the schematics to their product.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

[tabb...@gmail.com]

On Sunday, 12 May 2019 14:05:35 UTC+1, Cursitor Doom wrote:
> On Sun, 12 May 2019 11:04:06 +0000, Cursitor Doom wrote:
>
> [...]
>
> Sorry, guys, it's a Taylor 68A/M. I can't find the exact model on line
> but this one is as close as it gets:
>
> https://www.radiomuseum.org/r/taylor_afrf_signal_generator_68a_2.html
>
> The grid/Cathode bias does change with range selection; I just measured
> it. There doesn't seem anything obviously amiss with the readings:
>
> Range 8 (lowest frequency) -25V
> 7: -7V
> 6: -3.4V
> 5: -1V
> 4: -0.3V
> 3: -1.6V
> 2: -1.8V
> 1: -1.0
>
> Anode is +80 to +90VDC vs. Cathode over all ranges.

If you've eliminated other faults as possible then time to adjust the bias on the iffy range.


NT

[Cursitor Doom]

On Sun, 12 May 2019 08:46:42 -0700, tabbypurr wrote:

> If you've eliminated other faults as possible then time to adjust the
> bias on the iffy range.

It breaks my heart to do this, but I think it's a junker. On further
inspection some screwdriver jockey's fucked around with it and since I
only paid a fiver for it, it's time to consign it to recycling.

[Mike Coon]

In article <qb9fhd$gun$2...@dont-email.me>, cu...@notformail.com says...

>
> It breaks my heart to do this, but I think it's a junker. On further
> inspection some screwdriver jockey's fucked around with it and since I
> only paid a fiver for it, it's time to consign it to recycling.

The computer museum at Bletchley Park has (or had) a valve re-cycling
exchange. I bequeathed (or dumped) my father's collection of valves and
his (Taylor?) big wooden-cased valve tester to them and they made
appropriate gratitude noises...

Mike.

[Cursitor Doom]

On Sun, 12 May 2019 17:02:11 +0100, Mike Coon wrote:

> The computer museum at Bletchley Park has (or had) a valve re-cycling
> exchange. I bequeathed (or dumped) my father's collection of valves and
> his (Taylor?) big wooden-cased valve tester to them and they made
> appropriate gratitude noises...

Oh, I save the tubes alright; I'm not that much of a philistine.
That valve tester of yours was probably an AVO. I've got a couple of
those in my collection.

[Look165]

ECC81 is the same.

[Cursitor Doom]

On Sun, 12 May 2019 19:28:17 +0200, Look165 wrote:

> ECC81 is the same.

Yes, and fortunately I did have some spare new ones to try (on the
suggestion of a pal of mine who I would have ignored were it not for the
fact that he's 20 years my senior and has a doctorate in electronics). It
didn't fix the problem - unlike him I didn't expect it to - but did tend
to suggest that the issue was one of poor biasing (for whatever reason)
as I'd expected.
Sadly the thing has passed its prime by many years. It's not worth
continuing with when you discover the many and various pot cores have
nearly all been shattered by some dimwit who didn't know what he was
doing.

[Fox's Mercantile]

On 5/12/19 10:46 AM, tabb...@gmail.com wrote:
> On Sunday, 12 May 2019 14:05:35 UTC+1, Cursitor Doom wrote:
>> The grid/Cathode bias does change with range selection; I just measured
>> it. There doesn't seem anything obviously amiss with the readings:
>

> If you've eliminated other faults as possible then time to adjust the bias on the iffy range.

There is NO adjusting the bias. It's NOT adjustable.
The difference in readings is based on the difference in output for
each range. It's entirely likely it was like that new from the
factory.

[Cursitor Doom]

On Sun, 12 May 2019 12:49:21 -0500, Fox's Mercantile wrote:

> There is NO adjusting the bias. It's NOT adjustable.
> The difference in readings is based on the difference in output for each
> range. It's entirely likely it was like that new from the factory.

Whist it's true there are no trim pots involved, the fixed resistor
values will have changed over the last 65 years, which is quite possibly
responsible for the fault. They would need to be hooked out individually
and replaced, but it's not worth it.

[Ralph Mowery]

In article <-LqdnbRNIbQ8wUXB...@giganews.com>,
jda...@att.net says...

>
> There is NO adjusting the bias. It's NOT adjustable.
> The difference in readings is based on the difference in output for
> each range. It's entirely likely it was like that new from the
> factory.
>
>
>

Most likely the difference in the Q of the circuits and maybe the gain
of the tube at different frequencies. That would change the power of
the osicllator and voltages. One thing I would look at would be all the
reisitors in the generator. Those old carbon ones often change value
after a number of years, most seem to go up in value.

[Ralph Mowery]

In article <qb9m0d$gun$7...@dont-email.me>, cu...@notformail.com says...

> Sadly the thing has passed its prime by many years. It's not worth
> continuing with when you discover the many and various pot cores have
> nearly all been shattered by some dimwit who didn't know what he was
> doing.
>
>
>

In the past some coil problems have been caused by the change in the
cores. Not due to being shattered but just that the material ages.

[Mike Coon]

In article <qb9hfa$gun$3...@dont-email.me>, cu...@notformail.com says...

>
> That valve tester of yours was probably an AVO. I've got a couple of
> those in my collection.

Highly unlikely. I still have Dad's "Universal Avometer Model 7", so if
the valve tester was from the same stable I would have linked the two.
Unfortunately I can't find any record of my offer to Bletchley, to a
chap who IIRC has since died.

Mike.

[Cursitor Doom]

On Sun, 12 May 2019 22:00:16 +0100, Mike Coon wrote:

> Highly unlikely. I still have Dad's "Universal Avometer Model 7", so if
> the valve tester was from the same stable I would have linked the two.
> Unfortunately I can't find any record of my offer to Bletchley, to a
> chap who IIRC has since died.

I think you'll find AVO took over Taylor in the late 1950s so it's all
just about dates of manufacture.

[tabb...@gmail.com]

On Sunday, 12 May 2019 19:29:45 UTC+1, Cursitor Doom wrote:

> Whist it's true there are no trim pots involved, the fixed resistor
> values will have changed over the last 65 years, which is quite possibly
> responsible for the fault. They would need to be hooked out individually
> and replaced, but it's not worth it.

One needs replacing. Sounds like a trivial job. Send it to me if you want.


NT

[Mike Coon]

In article <qba4km$gun$9...@dont-email.me>, cu...@notformail.com says...

>
> On Sun, 12 May 2019 22:00:16 +0100, Mike Coon wrote:
>
> > Highly unlikely. I still have Dad's "Universal Avometer Model 7", so if
> > the valve tester was from the same stable I would have linked the two.
> > Unfortunately I can't find any record of my offer to Bletchley, to a
> > chap who IIRC has since died.
>
> I think you'll find AVO took over Taylor in the late 1950s so it's all
> just about dates of manufacture.

Oh, thanks, I might look that up. But the valve tester would certainly
be older than that. It did have a lacquered wooden case, after all!

Mike.

[Lucifer]

On Sun, 12 May 2019 11:04:06 -0000 (UTC), Cursitor Doom
<cu...@notformail.com> wrote:

>Gentlemen,
>
>I've got this RF sig gen I'm testing at the moment. It was made in 1955
>and is all valve (I say "all valve" but there are only two tubes in it
>and only one of those generates the RF - the other's 400Hz for the
>modulation).
>Anyway, it has 8 ranges in total covering 100KHz to 240Mhz. The
>oscillator tube is a double triode, a 12AT7. One half handles range from
>100Khz to 30Mhz and the other takes care of 30 - 240Mhz. Now, it all
>works great EXCEPT for one range (the 3rd lowest) which has appreciable
>distortion present on the output. It looks a bit like it's being over-
>driven on my scope. My question is, does a valve like a 12AT7 require
>different DC biasing points for every range of frequencies? Obviously the
>range switch is switching in different combinations of coils and
>capacitors, but is it likely to be also switching in different cathode-
>grid DC biasing at the same time?

I have a Radiosonde weather balloon transmitter which has a
single valve. The valve is a 3A5 twin triode with one being the
RF oscillator at 72 MHz and the other an audio oscillator which
was controlled by the sensors.

I did have a one valve test oscillator which was powered by
a nine volt grid bias battery.



>TIA

[Lucifer]

On Sun, 12 May 2019 15:53:17 -0000 (UTC), Cursitor Doom
<cu...@notformail.com> wrote:

>On Sun, 12 May 2019 08:46:42 -0700, tabbypurr wrote:
>
>> If you've eliminated other faults as possible then time to adjust the
>> bias on the iffy range.
>
>It breaks my heart to do this, but I think it's a junker. On further
>inspection some screwdriver jockey's fucked around with it and since I
>only paid a fiver for it, it's time to consign it to recycling.

I picked up a valve paging transmitter from a rubbish tip.
It was in working order, 5 watts output on 27.212 MHz,
with the crystal in an oven.

[Cursitor Doom]

On Mon, 13 May 2019 20:53:55 +1000, Lucifer wrote:

> I picked up a valve paging transmitter from a rubbish tip.
> It was in working order, 5 watts output on 27.212 MHz, with the crystal
> in an oven.

Nice find. It's amazing what gets thrown out! I dream of owning an
apartment overlooking a vast garbage tip so I can spot anything
potentially valuable being dumped. ;-)

[Cursitor Doom]

On Sun, 12 May 2019 18:12:10 -0700, tabbypurr wrote:

> One needs replacing. Sounds like a trivial job. Send it to me if you
> want.

Thanks for the offer, Tabs, but it's too far gone in other respects I'm
sorry to say. Trust me, I hate throwing anything away so it really has to
be terminal case for me to even consider junking it.

[Cursitor Doom]

On Mon, 13 May 2019 20:46:03 +1000, Lucifer wrote:

> I did have a one valve test oscillator which was powered by a nine volt
> grid bias battery.

Tust the grid alone was battery powered? Seems a bit of a strange idea. I
mean, it's entirely feasible, but if you have to generate higher voltages
for the anode from the mains....

[Lucifer]

On Mon, 13 May 2019 11:31:05 -0000 (UTC), Cursitor Doom
<cu...@notformail.com> wrote:

>On Mon, 13 May 2019 20:46:03 +1000, Lucifer wrote:
>
>> I did have a one valve test oscillator which was powered by a nine volt
>> grid bias battery.
>
>Tust the grid alone was battery powered? Seems a bit of a strange idea. I
>mean, it's entirely feasible, but if you have to generate higher voltages
>for the anode from the mains....

The nine volts was the anode voltage!
I had a hybrid car radio with 4 valves and 2 transistors.
The valves used the 12 volts for the anode voltage.

Valves don't need high voltage on the anode for low power
applications.

[Lucifer]

On Mon, 13 May 2019 11:23:51 -0000 (UTC), Cursitor Doom
<cu...@notformail.com> wrote:

>On Mon, 13 May 2019 20:53:55 +1000, Lucifer wrote:
>
>> I picked up a valve paging transmitter from a rubbish tip.
>> It was in working order, 5 watts output on 27.212 MHz, with the crystal
>> in an oven.
>
>Nice find. It's amazing what gets thrown out! I dream of owning an
>apartment overlooking a vast garbage tip so I can spot anything
>potentially valuable being dumped. ;-)

I have found so many amazing things at tips.
A bag of stained glass hobby bits and pieces.
Photo copiers I spent hours dismantling.

Auctions are a good cheap source of what many people call junk.

[Cursitor Doom]

On Mon, 13 May 2019 21:52:09 +1000, Lucifer wrote:

> I have found so many amazing things at tips.
> A bag of stained glass hobby bits and pieces.
> Photo copiers I spent hours dismantling.
>
> Auctions are a good cheap source of what many people call junk.

What's worth salvaging from old photocopiers? I vaguely recall there's
some exotic goodies in them somewhere.

[Cursitor Doom]

On Mon, 13 May 2019 21:46:56 +1000, Lucifer wrote:

> The nine volts was the anode voltage!
> I had a hybrid car radio with 4 valves and 2 transistors.
> The valves used the 12 volts for the anode voltage.
>
> Valves don't need high voltage on the anode for low power applications.

I'll have to look into that. I had no idea of such extraordinarily low
plate voltages as that. 9V eh? Wow! Do you happen to remember the type
number of those? I'd be fascinated to check out the data sheet for 'em.

[Fox's Mercantile]

<http://www.junkbox.com/electronics/lowvoltagetubes.shtml>

[Ralph Mowery]

In article <qbbusf$p45$2...@dont-email.me>, cu...@notformail.com says...

>
> I'll have to look into that. I had no idea of such extraordinarily low
> plate voltages as that. 9V eh? Wow! Do you happen to remember the type
> number of those? I'd be fascinated to check out the data sheet for 'em.
>
>
>

At one time the car radios had low voltage tubes in them that just ran
on 12 volts . They could not supply the power for the audio output, so
a transisitor or two were used in the audio stages. Tubes worked well
for the radio frequency signals and transistors not so well in those
years.

Back in the eairly 1960's I built a one tube receiver for the airplanes
that ran on 12 volts only. Plans were in a Popular Electronics of the
same years. Had to use earphones for it.

[Wond]

On Mon, 13 May 2019 14:23:35 +0000, Cursitor Doom wrote:

> On Mon, 13 May 2019 21:52:09 +1000, Lucifer wrote:
>
>> I have found so many amazing things at tips. A bag of stained glass
>> hobby bits and pieces. Photo copiers I spent hours dismantling.
>>
>> Auctions are a good cheap source of what many people call junk.
>
> What's worth salvaging from old photocopiers? I vaguely recall there's
> some exotic goodies in them somewhere.

In a good copier, there's an excellent lens, for a start.

[Cursitor Doom]

On Mon, 13 May 2019 10:57:54 -0400, Ralph Mowery wrote:

> Back in the eairly 1960's I built a one tube receiver for the airplanes
> that ran on 12 volts only. Plans were in a Popular Electronics of the
> same years. Had to use earphones for it.

Those awful high impedance ones, by any chance?

[Cursitor Doom]

On Mon, 13 May 2019 09:39:11 -0500, Fox's Mercantile wrote:

> <http://www.junkbox.com/electronics/lowvoltagetubes.shtml>

Thanks!

[Ralph Mowery]

In article <qbc3mj$p45$3...@dont-email.me>, cu...@notformail.com says...

>
> > Back in the eairly 1960's I built a one tube receiver for the airplanes
> > that ran on 12 volts only. Plans were in a Popular Electronics of the
> > same years. Had to use earphones for it.
>
> Those awful high impedance ones, by any chance?
>
>
>
>

Some of the older ones that were around 1000 ohms or more impedance
phones. The lower ones would not work.

[Mike Coon]

In article <MPG.374358d...@news.plus.net>,
gra...@mjcoon.plus.com says...

See https://www.radiomuseum.org/r/taylor_valve_tester_47a47.html

Mike.

[Cursitor Doom]

On Mon, 13 May 2019 18:14:29 +0100, Mike Coon wrote:

> See https://www.radiomuseum.org/r/taylor_valve_tester_47a47.html

Very nice, that. You should hang on to it; valves seem to be making a
comeback in some areas.

[Clifford Heath]

On 14/5/19 12:23 am, Cursitor Doom wrote:
> On Mon, 13 May 2019 21:52:09 +1000, Lucifer wrote:
> What's worth salvaging from old photocopiers? I vaguely recall there's
> some exotic goodies in them somewhere.

Perhaps not exotic, but they tend to have a few nice 24V motors.

[Lucifer]

On Mon, 13 May 2019 14:27:27 -0000 (UTC), Cursitor Doom
<cu...@notformail.com> wrote:

>On Mon, 13 May 2019 21:46:56 +1000, Lucifer wrote:
>
>> The nine volts was the anode voltage!
>> I had a hybrid car radio with 4 valves and 2 transistors.
>> The valves used the 12 volts for the anode voltage.
>>
>> Valves don't need high voltage on the anode for low power applications.
>
>I'll have to look into that. I had no idea of such extraordinarily low
>plate voltages as that. 9V eh? Wow! Do you happen to remember the type
>number of those? I'd be fascinated to check out the data sheet for 'em.

I don't remember other that the car radio used transistors for the
second audio and the audio output and valves for the rest.

[Lucifer]

On Mon, 13 May 2019 09:39:11 -0500, Fox's Mercantile <jda...@att.net>
wrote:

Very interesting. Thank you.

[Mike Coon]

In article <qbcafc$6ea$1...@dont-email.me>, cu...@notformail.com says...

>
> On Mon, 13 May 2019 18:14:29 +0100, Mike Coon wrote:
>
> > See https://www.radiomuseum.org/r/taylor_valve_tester_47a47.html
>
> Very nice, that. You should hang on to it; valves seem to be making a
> comeback in some areas.

Too late; assuming they have not thrown it away, it has been at
Bletchley Park for several years, hopefully supporting their old
computer resusitation projects.

Mike.

[Cursitor Doom]

I was trying to remember what exactly it was last night. I *think*
there's a EHT generator in there to attract the 'soot' to the paper that
can be easily converted into a 60kV taser. But I might easily be
mistaken, so don't quote me on that.

[Cursitor Doom]

On Tue, 14 May 2019 17:26:55 +0100, Mike Coon wrote:

> Too late; assuming they have not thrown it away, it has been at
> Bletchley Park for several years, hopefully supporting their old
> computer resusitation projects.
>
> Mike.

I really must get around to visiting that place some time. I've heard
very good reports of it.

[three_jeeps]

It's a shame that mostly all the links in the project section point to sites that are gone....

[three_jeeps]

yes, motors, drive pullies, belts, lead screws, stepper motors, microswitches,

[John Robertson]

http://web.archive.org

John ;-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

[Michael Terrell]

On Sunday, May 12, 2019 at 7:04:09 AM UTC-4, Cursitor Doom wrote:
> Gentlemen,
>
> I've got this RF sig gen I'm testing at the moment. It was made in 1955
> and is all valve (I say "all valve" but there are only two tubes in it
> and only one of those generates the RF - the other's 400Hz for the
> modulation).
> Anyway, it has 8 ranges in total covering 100KHz to 240Mhz. The
> oscillator tube is a double triode, a 12AT7. One half handles range from
> 100Khz to 30Mhz and the other takes care of 30 - 240Mhz. Now, it all
> works great EXCEPT for one range (the 3rd lowest) which has appreciable
> distortion present on the output. It looks a bit like it's being over-
> driven on my scope. My question is, does a valve like a 12AT7 require
> different DC biasing points for every range of frequencies? Obviously the
> range switch is switching in different combinations of coils and
> capacitors, but is it likely to be also switching in different cathode-
> grid DC biasing at the same time?
>
> TIA

These simple generators were intentionally distorted. They were over driven for three reasons.

The first was to make sure that the output didn't drop out and kill the oscillation at the high end of each band.

The second was to produce harmonics on the higher bands.

The third was to allow the unit to continue to operate as the tube aged. As far as the coils failing, some adsorbed moisture, which lowered their 'Q'.

Often, the 400 or 1,000 Hz tone was distorted, as well due to the lack of AGC. It gave a distinct sound in the receiver being aligned. Look at what HP did in their 606 and 608 series generators to produce a clean signal. They certainly didn't attempt to do it with two tubes!

I remember the low voltage tubes in car radios. They weren't used for very long. It was an attempt to eliminate the Vibrator derived HV plate supply, without using the more expensive transistors of their day. I think that Philco/Ford went that route, while Delco and Motorola went straight to all transistor designs. For used Philco, Bendix and Motorola radios in the '60s and '70a. BTW, Galvin Manufacturing invented the car radio, then they changed their name to Motorola to reflect their main product line.

[John Robertson]

I thought the first car radio was back in the early 20s....seem to
recall seeing a picture in a magazine or old encyclopedia (I used to
read those for fun as a kid) in the 60s.

The Galvin/Motorola was the first commercially successful radio. Nice to
know where that famous name came from, thanks!

https://en.wikipedia.org/wiki/Vehicle_audio speaks of a car radio in
1924 in NSW, Australia.


John :-#)#

[Michael Terrell]

I had never heard of the 1924 radio. Was it a real car radio, or a battery powered radio installed in a car? I also remember one of the old Roy Rogers TV show episodes with a battery powered radio on a horse that they used to catch the bad guys. I saw that over 50 years ago. ;-)

I remember when Bendix switched from TO-3 output transistors, to TO-220. Despite the warnings not to bend the leads at the case, they did. They had over a double digit failure rate within two months of the cars being sold. They used a tiny daughter board, and mounted it in one of the holes for the original package. They were very shitty radios. :(

[John Robertson]

On 2019/05/15 7:51 p.m., Michael Terrell wrote:
> On Wednesday, May 15, 2019 at 9:38:42 PM UTC-4, John Robertson wrote:
>> On 2019/05/15 6:02 p.m., Michael Terrell wrote:
>>> On Sunday, May 12, 2019 at 7:04:09 AM UTC-4, Cursitor Doom wrote:
>>>> Gentlemen,
>>>>
>>>> I've got this RF sig gen I'm testing at the moment. It was made in 1955
>>>> and is all valve (I say "all valve" but there are only two tubes in it
>>>> and only one of those generates the RF - the other's 400Hz for the
>>>> modulation).
>>>> Anyway, it has 8 ranges in total covering 100KHz to 240Mhz. The
>>>> oscillator tube is a double triode, a 12AT7. One half handles range from
>>>> 100Khz to 30Mhz and the other takes care of 30 - 240Mhz. Now, it all
>>>> works great EXCEPT for one range (the 3rd lowest) which has appreciable
>>>> distortion present on the output. It looks a bit like it's being over-
>>>> driven on my scope. My question is, does a valve like a 12AT7 require
>>>> different DC biasing points for every range of frequencies? Obviously the
>>>> range switch is switching in different combinations of coils and
>>>> capacitors, but is it likely to be also switching in different cathode-
>>>> grid DC biasing at the same time?
>>>>
>>>> TIA
>>>
>>> These simple generators were intentionally distorted. They were over driven for three reasons.
>>>
>>> The first was to make sure that the output didn't drop out and kill the oscillation at the high end of each band.
>>>
>>> The second was to produce harmonics on the higher bands.
>>>

>>> The third was to allow the unit to continue to operate as the tube aged.. As far as the coils failing, some adsorbed moisture, which lowered their 'Q'.

>>>
>>> Often, the 400 or 1,000 Hz tone was distorted, as well due to the lack of AGC. It gave a distinct sound in the receiver being aligned. Look at what HP did in their 606 and 608 series generators to produce a clean signal. They certainly didn't attempt to do it with two tubes!
>>>
>>> I remember the low voltage tubes in car radios. They weren't used for very long. It was an attempt to eliminate the Vibrator derived HV plate supply, without using the more expensive transistors of their day. I think that Philco/Ford went that route, while Delco and Motorola went straight to all transistor designs. For used Philco, Bendix and Motorola radios in the '60s and '70a. BTW, Galvin Manufacturing invented the car radio, then they changed their name to Motorola to reflect their main product line.
>>>
>>
>> I thought the first car radio was back in the early 20s....seem to
>> recall seeing a picture in a magazine or old encyclopedia (I used to
>> read those for fun as a kid) in the 60s.
>>
>> The Galvin/Motorola was the first commercially successful radio. Nice to
>> know where that famous name came from, thanks!
>>
>> https://en.wikipedia.org/wiki/Vehicle_audio speaks of a car radio in
>> 1924 in NSW, Australia.
>
> I had never heard of the 1924 radio. Was it a real car radio, or a battery powered radio installed in a car? I also remember one of the old Roy Rogers TV show episodes with a battery powered radio on a horse that they used to catch the bad guys. I saw that over 50 years ago. ;-)

I think it was more likely a battery radio that someone jammed into a
car. I have a RCA 24 in my collection of early 20's radios that was an
early luggable battery radio. Used a few WD-11s and had two spares in a
holder - I imagine the tubes did not like being bounced around so spares
were really needed!

>
> I remember when Bendix switched from TO-3 output transistors, to TO-220. Despite the warnings not to bend the leads at the case, they did. They had over a double digit failure rate within two months of the cars being sold. They used a tiny daughter board, and mounted it in one of the holes for the original package. They were very shitty radios. :(
>

I had little to do with car radios, mostly I played with home battery
radios as a teenager.

How that led to pinball and jukebox sales and service is a mystery...

(well, not really, I LIKE fixing things!)

[tabb...@gmail.com]

The 1924 radio was experimental. Imagine trying to get stable reception with a mobile positive feedback circuit set to the brink of oscillation, powered by either HT dry batteries or a vibrator PSU. Plus the thing had a huge aerial rig over the car. It wasn't a practical commercial proposition.

Of course you can lose the PFB and have a row of valves, but then your HT battery drain is far worse.


NT

[Cursitor Doom]

On Wed, 15 May 2019 18:02:53 -0700, Michael Terrell wrote:

> These simple generators were intentionally distorted. They were over
> driven for three reasons.
>
> The first was to make sure that the output didn't drop out and kill the
> oscillation at the high end of each band.
>
> The second was to produce harmonics on the higher bands.
>
> The third was to allow the unit to continue to operate as the tube aged.
> As far as the coils failing, some adsorbed moisture, which lowered their
> 'Q'.
>
> Often, the 400 or 1,000 Hz tone was distorted, as well due to the lack
> of AGC. It gave a distinct sound in the receiver being aligned. Look at
> what HP did in their 606 and 608 series generators to produce a clean
> signal. They certainly didn't attempt to do it with two tubes!

Very interesting, thanks!