Converting Tube Amp To Solid State

[Bob Griffin]

I would like some advice please on how to convert this tube amp to all
solid state.

https://app.box.com/s/1h1dpmjv07kosec832ud7kqs7tw7kcu1

It is supposedly an audio amp that oscillates in the MHz region
thereby producing its own transmission carrier.

The coupling coils are air core.

I would like to run this off 12VAC with an output of about 10W. Note
the tubes are fed directly with AC.

Yes, I know the output is nasty. This is just for an experiment.

To miantain the same specs, what transistors or FET's should I use?

What else in the componentry needs to be modified?

I will draw a circuit diagram based upon the recommendations here.

Many thanks,

Bob Griffin

[Jeff Liebermann]

On Mon, 25 Jan 2016 17:46:48 +1100, Bob Griffin
<bgri...@cybernode.com> wrote:

>I would like some advice please on how to convert this tube amp to all
>solid state.
>
>https://app.box.com/s/1h1dpmjv07kosec832ud7kqs7tw7kcu1
>
>It is supposedly an audio amp that oscillates in the MHz region
>thereby producing its own transmission carrier.

Using MOSFET's and JFET's to replace tubes has been around since the
devices were invented.
<http://www.qsl.net/kh6grt/page4/tubesters/MOSFETs%20for%20Tubes.pdf>
There's a commercial version called a "FETRON".
<http://www.philipstorr.id.au/radio/eleven/fetron.htm>
<https://www.google.com/search?q=fetron&tbm=isch>
I have one of these, unfortunately with a blown JFET.
<http://www.vintage-radio.net/forum/showthread.php?t=62814>
<http://www.vintage-radio.net/forum/attachment.php?attachmentid=43883&d=1292198107>

>The coupling coils are air core.
>
>I would like to run this off 12VAC with an output of about 10W. Note
>the tubes are fed directly with AC.
>
>Yes, I know the output is nasty. This is just for an experiment.
>
>To miantain the same specs, what transistors or FET's should I use?
>
>What else in the componentry needs to be modified?
>
>I will draw a circuit diagram based upon the recommendations here.
>
>Many thanks,
>
>Bob Griffin

I can't answer your questions without analyzing the original tube
circuit. That won't help because you're missing all the bypass
capacitors, missing all the grid bias resistors, missing all the
resistors from cathode to ground, don't have any values for the
inductors, and have the wrong number for the 6SJ7. 6.3v AC on the
output triode will do a fine job of AM modulating your output with 60
Hz. In other words, it won't work. It looks like a schematic created
with LTspice. Have you run a simulation to see if the tube version
works?

Methinks you will be better off designing your solid state circuit
from scratch.



--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Jeff Liebermann]

On Mon, 25 Jan 2016 00:00:32 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

>I can't answer your questions without analyzing the original tube
>circuit. That won't help because you're missing all the bypass
>capacitors, missing all the grid bias resistors, missing all the
>resistors from cathode to ground, don't have any values for the
>inductors, and have the wrong number for the 6SJ7. 6.3v AC on the
>output triode will do a fine job of AM modulating your output with 60
>Hz. In other words, it won't work. It looks like a schematic created
>with LTspice. Have you run a simulation to see if the tube version
>works?

I missed a few more things. The plate voltages should not be 125VAC
but rather 125VDC. All the coils will probably require some form of
tuning capacitors. The approximate turns ratio of the first 2
transformers might be close, but the output stage is backwards. The
tube output impedance is much higher than the load (presumably 50
ohms), so more turns would be needed on the plate side, than on the
load side.

Also, why are you specifying metal can tubes? They're not very
reliable, get rather hot, and are difficult to find in working
condition.

[Tauno Voipio]

Jeff, you did not notice the real source of raw hum (buzz): The
plates are fed with raw AC, running the thing in self-rectifying mode.

The design is sick - forget it:

- there are no by-pass capacitors,
- there is no explicit resonance or feedback for oscillation,
- there is no output matching,
- the pentode tubes are obviously incorrect (maybe 6SJ7GT),
- the tubes were ancient already 50 years ago.

--

-TV

[Tauno Voipio]

On 25.1.16 10:13, Jeff Liebermann wrote:
> On Mon, 25 Jan 2016 00:00:32 -0800, Jeff Liebermann <je...@cruzio.com>
> wrote:
>
>> I can't answer your questions without analyzing the original tube
>> circuit. That won't help because you're missing all the bypass
>> capacitors, missing all the grid bias resistors, missing all the
>> resistors from cathode to ground, don't have any values for the
>> inductors, and have the wrong number for the 6SJ7. 6.3v AC on the
>> output triode will do a fine job of AM modulating your output with 60
>> Hz. In other words, it won't work. It looks like a schematic created
>> with LTspice. Have you run a simulation to see if the tube version
>> works?
>
> I missed a few more things. The plate voltages should not be 125VAC
> but rather 125VDC. All the coils will probably require some form of
> tuning capacitors. The approximate turns ratio of the first 2
> transformers might be close, but the output stage is backwards. The
> tube output impedance is much higher than the load (presumably 50
> ohms), so more turns would be needed on the plate side, than on the
> load side.
>
> Also, why are you specifying metal can tubes? They're not very
> reliable, get rather hot, and are difficult to find in working
> condition.
>
>> Methinks you will be better off designing your solid state circuit
>>from scratch.

6SJ7GT is a glass tube (GT), but an ancient octal-based one.

--

-TV

[tabb...@gmail.com]

On Monday, 25 January 2016 06:47:00 UTC, Bob Griffin wrote:
> I would like some advice please on how to convert this tube amp to all
> solid state.
>
> https://app.box.com/s/1h1dpmjv07kosec832ud7kqs7tw7kcu1

don't. There is no other good advice.

> It is supposedly an audio amp that oscillates in the MHz region
> thereby producing its own transmission carrier.

it isn't. It's a mad mess.


NT

[Jeff Liebermann]

On Mon, 25 Jan 2016 14:23:28 +0200, Tauno Voipio
<tauno....@notused.fi.invalid> wrote:

>On 25.1.16 10:13, Jeff Liebermann wrote:
>> On Mon, 25 Jan 2016 00:00:32 -0800, Jeff Liebermann <je...@cruzio.com>
>> wrote:
>> Also, why are you specifying metal can tubes? They're not very
>> reliable, get rather hot, and are difficult to find in working
>> condition.

>6SJ7GT is a glass tube (GT), but an ancient octal-based one.

Sorry. I didn't notice the GT suffix. It comes in both metal can and
glass varieties:
<http://www.jacmusic.com/images/Werbung/6SJ7.jpg>
<https://www.vintagetools.de/out/pictures/master/product/1/RCA_6SJ7.jpg>
<http://cdn.shopify.com/s/files/1/0333/7633/products/6sj7nup1_e16601b4-5bd2-48b5-8fe7-9743c17d0260_large.jpg?v=1415081779>

[bitrex]

tabb...@gmail.com Wrote in message:

Agree +1

Newsgroups need a "like" button for posts..

--


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

[Jim Thompson]

On Mon, 25 Jan 2016 12:07:37 -0500 (EST), bitrex
<bit...@de.lete.earthlink.net> wrote:

>tabb...@gmail.com Wrote in message:
>> On Monday, 25 January 2016 06:47:00 UTC, Bob Griffin wrote:
>>> I would like some advice please on how to convert this tube amp to all
>>> solid state.
>>>
>>> https://app.box.com/s/1h1dpmjv07kosec832ud7kqs7tw7kcu1
>>
>> don't. There is no other good advice.
>>
>>> It is supposedly an audio amp that oscillates in the MHz region
>>> thereby producing its own transmission carrier.
>>
>> it isn't. It's a mad mess.
>>
>>
>> NT
>>
>
>Agree +1
>
>Newsgroups need a "like" button for posts..

shift+ctrl+S kills the thread

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

[Bob Griffin]

On Mon, 25 Jan 2016 00:13:02 -0800, Jeff Liebermann <je...@cruzio.com>

wrote:

>On Mon, 25 Jan 2016 00:00:32 -0800, Jeff Liebermann <je...@cruzio.com>
>wrote:
>
>>I can't answer your questions without analyzing the original tube
>>circuit. That won't help because you're missing all the bypass
>>capacitors, missing all the grid bias resistors, missing all the
>>resistors from cathode to ground, don't have any values for the
>>inductors, and have the wrong number for the 6SJ7. 6.3v AC on the
>>output triode will do a fine job of AM modulating your output with 60
>>Hz. In other words, it won't work. It looks like a schematic created
>>with LTspice. Have you run a simulation to see if the tube version
>>works?
>
>I missed a few more things. The plate voltages should not be 125VAC
>but rather 125VDC. All the coils will probably require some form of
>tuning capacitors. The approximate turns ratio of the first 2
>transformers might be close, but the output stage is backwards. The
>tube output impedance is much higher than the load (presumably 50
>ohms), so more turns would be needed on the plate side, than on the
>load side.
>
>Also, why are you specifying metal can tubes? They're not very
>reliable, get rather hot, and are difficult to find in working
>condition.
>
>>Methinks you will be better off designing your solid state circuit
>>from scratch.

Thank you Jeff for your expert opinion.

Yes, I know that, by conventional standards, there are missing
components, irregularities etc.

I am happy to report that I did not design this circuit. It is of
historical interest relating to quack medical therapy.

I could not find the specified tubes and instead wanted to replicate
it in solid state to see what the output might actually look like.

If someone can tell me, perhaps this would save me the trouble.

Then again, I am interested it how it could be converted to solid
state, mostly as a learning experience. I don't expect it will perform
any useful function other than that.

Bob Griffin

[Tim Williams]

"Bob Griffin" <bgri...@cybernode.com> wrote in message
news:okddabp3d3qg873a9...@4ax.com...

> I am happy to report that I did not design this circuit. It is of
> historical interest relating to quack medical therapy.
>
> I could not find the specified tubes and instead wanted to replicate
> it in solid state to see what the output might actually look like.
>
> If someone can tell me, perhaps this would save me the trouble.
>
> Then again, I am interested it how it could be converted to solid
> state, mostly as a learning experience. I don't expect it will perform
> any useful function other than that.

Well, that's no challenge at all, Bob!

There seems, perhaps, the impression that "you don't really know until you
build it" -- that a device has some magic power by nature of its existence,
perhaps imbued through the act of creation that made it.

Fortunately, in electronics, we have no need of that whatsoever! We can
fully express the behavior of any* circuit, because that circuit must obey
very well understood physical laws.

*Mumble mumble Goedel something or other. :)

Now, that does assume having complete knowledge of the circuit. There are
many electrical details lacking. What were the dimensions of the coils?
Was the wiring short and optimal (as an RF engineer would wire it), or was
it laid out on plywood with Fahnestock clips and bailing wire? What was the
frequency range, waveform, amplitude and so on of the input? What was the
load, how was it connected and used?

Taking it at face value, and assuming modest construction and coil
dimensions, it would probably have some gain (perhaps enough to oscillate on
its own) at some points during the supply voltage cycle, and so would be
expected to output pulsating bursts of RF, at whatever frequency the coils
are tuned to.

The output power would be quite weak, unless matched into a fairly high
impedance, in which case perhaps a tenth of a watt might be available (and
even then, probably peak, not average). In application to biological
material, it would do absolutely, positively nothing, at any point in the
waveform, for any input.

Perhaps if constructed in a sufficiently imposing manner, it would be
capable of impressing (or scaring) the patient into some psychosomatic
effect, which isn't to say it has no effect whatsoever, but such an effect
could be had with much simpler (if not necessarily simpler-looking),
non-electrical equipment.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com

[Jon Elson]

Bob Griffin wrote:


>
> I am happy to report that I did not design this circuit. It is of
> historical interest relating to quack medical therapy.
>

Ah, well, it is quack electrical engineering, too! Note that there is no
proper bias on ANY of the tubes. In general, they would conduct about full-
on during the positive half cycles of the mains. Since they have quite
large plate resistors, the tubes won't burn up, but unless the thing is fed
lots of input signal, the tubes won't produce much output other than the 60
Hz from the AC plate supply. I see no reason it would oscillate, either, as
there is no feedback path anywhere, unless there is some coupling between
coils that is not in the drawing.

Looks like a total scam. Since it will NOT do anything as drawn, trying to
make a non-working circuit with transistors out of a non-working tube
schematic will not get you very far.

Jon

[Jeff Liebermann]

On Tue, 26 Jan 2016 11:05:28 +1100, Bob Griffin
<bgri...@cybernode.com> wrote:

>I am happy to report that I did not design this circuit. It is of
>historical interest relating to quack medical therapy.

Sigh. Quack medical electronics... you came to the right place.
Note that the circuit will not do anything useful as drawn. You
obviously have the use of LTspice. Run the simulation and see for
yourself.

>I could not find the specified tubes and instead wanted to replicate
>it in solid state to see what the output might actually look like.

I probably have both types. I'll look.

Also see eBay:
<http://www.ebay.com/sch/i.html?_nkw=6sn7+tube+-socket>
<http://www.ebay.com/sch/i.html?_nkw=6c5+tube+-socket>
If you want it to work, buy a spare as tubes that old are often dead
or dying.

>Then again, I am interested it how it could be converted to solid
>state, mostly as a learning experience. I don't expect it will perform
>any useful function other than that.

Several of the URL's I previously listed included some theory and same
circuits for using a FET to replace a tube. Those should be a good
start.

[tabb...@gmail.com]

On Tuesday, 26 January 2016 03:59:10 UTC, Jeff Liebermann wrote:
> On Tue, 26 Jan 2016 11:05:28 +1100, Bob Griffin
> <bgri...@cybernode.com> wrote:

big snips

> Several of the URL's I previously listed included some theory and same
> circuits for using a FET to replace a tube. Those should be a good
> start.

but be aware that putting -400v or whatever it was onto a solid state amp may go badly very rapidly. Valves are tough things, trannies not one bit.


NT

[Bob Griffin]

On Mon, 25 Jan 2016 19:54:04 -0600, "Tim Williams"
<tiw...@seventransistorlabs.com> wrote:


>Fortunately, in electronics, we have no need of that whatsoever! We can
>fully express the behavior of any* circuit, because that circuit must obey
>very well understood physical laws.
>

The schematic was done in Diptrace not LTSpice, so I have not run it.
I would not know how to hanlde the probable convergence errors anyway.

>*Mumble mumble Goedel something or other. :)
>
>Now, that does assume having complete knowledge of the circuit. There are
>many electrical details lacking. What were the dimensions of the coils?
>Was the wiring short and optimal (as an RF engineer would wire it), or was
>it laid out on plywood with Fahnestock clips and bailing wire? What was the
>frequency range, waveform, amplitude and so on of the input? What was the
>load, how was it connected and used?
>

As far as I know it was built upon a shielded chassis. The air coils
were in cans. But due to the lack of bypass caps, etc., I suspect it
was intended to oscillate. The guy who designed it would have been at
least as smart to know that.

>Taking it at face value, and assuming modest construction and coil
>dimensions, it would probably have some gain (perhaps enough to oscillate on
>its own) at some points during the supply voltage cycle, and so would be
>expected to output pulsating bursts of RF, at whatever frequency the coils
>are tuned to.
>

Is there any indication in the schematic that the coils are tuned to a
particular frequency?

>The output power would be quite weak, unless matched into a fairly high
>impedance, in which case perhaps a tenth of a watt might be available (and
>even then, probably peak, not average). In application to biological
>material, it would do absolutely, positively nothing, at any point in the
>waveform, for any input.

As I understand it was connected to the subject via hand-held
electrodes.

Sorry but these things just fascinate me.

Bob Griffin

[tabb...@gmail.com]

On Monday, 25 January 2016 06:47:00 UTC, Bob Griffin wrote:

> I would like some advice please on how to convert this tube amp to all
> solid state.
>
> https://app.box.com/s/1h1dpmjv07kosec832ud7kqs7tw7kcu1
>
> It is supposedly an audio amp that oscillates in the MHz region
> thereby producing its own transmission carrier.
>
> The coupling coils are air core.
>
> I would like to run this off 12VAC with an output of about 10W. Note
> the tubes are fed directly with AC.
>
> Yes, I know the output is nasty. This is just for an experiment.
>
> To miantain the same specs, what transistors or FET's should I use?
>
> What else in the componentry needs to be modified?

To answer the question as is, solid state parts do not behave like valves, especially pentodes, no matter what you do with them. If you're looking for nonobvious behaviour, you ned to use the parts specified and not change it.


NT

[tabb...@gmail.com]

On Tuesday, 26 January 2016 06:14:48 UTC, Bob Griffin wrote:
> On Mon, 25 Jan 2016 19:54:04 -0600, "Tim Williams"
> <tiw...@seventransistorlabs.com> wrote:

> As far as I know it was built upon a shielded chassis. The air coils
> were in cans. But due to the lack of bypass caps, etc., I suspect it
> was intended to oscillate. The guy who designed it would have been at
> least as smart to know that.

The supply rail is presumably of very low impedance, and freedom from mains borne noise probably not a concern, so it might not need decoupling caps.

> >Taking it at face value, and assuming modest construction and coil
> >dimensions, it would probably have some gain (perhaps enough to oscillate on
> >its own) at some points during the supply voltage cycle, and so would be
> >expected to output pulsating bursts of RF, at whatever frequency the coils
> >are tuned to.
> >
>
> Is there any indication in the schematic that the coils are tuned to a
> particular frequency?

not explicitly. But all Ls have C, and all LCs are tuned, like it or not. It looks like all 3 transformers are the same, so most likely having the same tuned frequency, give or take some tolerance.

> >The output power would be quite weak, unless matched into a fairly high
> >impedance, in which case perhaps a tenth of a watt might be available (and
> >even then, probably peak, not average). In application to biological
> >material, it would do absolutely, positively nothing, at any point in the
> >waveform, for any input.
>
> As I understand it was connected to the subject via hand-held
> electrodes.
>
> Sorry but these things just fascinate me.
>
> Bob Griffin

I expect if it passed through the subject, through a neon to ground it would raise the subject's heart rate at least.

We don't know if the output feeds back to the input via some path, but it's quite likely. Even if you only get gains of 10 per valve that adds up to a gain of 10x10x10x4x4x4 = 64,000. Rather more at resonance.


NT

[Tauno Voipio]

On the contrary - it is often much easier to make non-working
pieces of electronics, I have made plenty of them in the last
50 years.

I hope that there has been a transformer between the mains supply
and the 125 VAC plate feed.

--

-TV

[tabb...@gmail.com]

On Tuesday, 26 January 2016 14:02:55 UTC, Tauno Voipio wrote:
> On 26.1.16 05:08, Jon Elson wrote:
> > Bob Griffin wrote:

> >> I am happy to report that I did not design this circuit. It is of
> >> historical interest relating to quack medical therapy.

> I hope that there has been a transformer between the mains supply
> and the 125 VAC plate feed.

Why do I doubt it.


NT

[Tim Williams]

"Bob Griffin" wrote in message
news:j83eablau43foftuo...@4ax.com...

> Is there any indication in the schematic that the coils are tuned to a
> particular frequency?

No. That depends entirely on the dimensions of the coils and their
parasitic capacitance, and the capacitance (including Miller effect) of
the tubes.

Hence my comment about imperfect knowledge. :)