6DW5 vs. 6BQ5/EL84

[Alejandro Lieber]

Why is it that the 6DW5 is not used any longer in PP audio amplifiers.

A pair can output 30 watts vs 17 watts for a pair of 6BQ5 /EL84.

The price of the 6DW5 is a third of the 6BQ5.

I remember adjusting the different bias of my father's BOGEN DB230 40
years ago. A 7199 drove a pair of 6DW5.
--
Alejandro Lieber LU1FCR
Rosario Argentina

Real-Time F2-Layer Critical Frequency Map foF2:
http://1fcr.com.ar

[flipper]

On Wed, 15 Feb 2012 01:34:23 +0000 (UTC), Alejandro Lieber
<inv...@not-for-mail.invalid> wrote:

>Why is it that the 6DW5 is not used any longer in PP audio amplifiers.
>
>A pair can output 30 watts vs 17 watts for a pair of 6BQ5 /EL84.
>
>The price of the 6DW5 is a third of the 6BQ5.
>
>I remember adjusting the different bias of my father's BOGEN DB230 40
>years ago. A 7199 drove a pair of 6DW5.

As for 'today' it's probably because people tend to copy what was
common or 'popular' and that's not a bad starting place since there
was probably some good reason why it was. The 6DW5 datasheet also
doesn't give any audio amp numbers so DIYers don't have an 'easy' spec
to go by.

As for 'back then' your comparison doesn't hold because the 6DW5
wasn't less expensive than the 6BQ5 and my 1961 RCA price sheet lists
it as $3.20 vs $2.25, or 42% more expensive. Second, it needs a lower,
regulated, screen and, in the Bogen, that sucks up the cost of a 6CM7
regulator.

The Bogen is also operating them at 435V, when Design Max specs 330V,
and Class B which, assuming one doesn't mind Class B, requires the
added complexity of fixed bias.

In short, it isn't at all clear that's 'better' than a pair of 6L6GCs,
and a plain ole simple B+ power supply, which could go up to 55 Watts
Class AB or around 30 Watts Class AB UL for not much more tube cost
(saving the 6CM7, alone, pays for the cost of one pair over the 6DW5).

At any rate, a plain ole 6BQ5 PP amp would have certainly been less
expensive not only in tube cost but the heater and B+power supplies
and OPTs. Plus, 17/15 Watts is only 3 dB less than 30 Watts which,
from a practical standpoint, doesn't really make all that much of a
difference so the cost benefit ratio definitely favors the 6BQ5, which
is probably why they were pretty common.

Now, another 'not seen very often today' tube is the 6CW5, which can
do 25 Watts 'in spec' Class AB, but it also takes a lower screen
supply. But it's a good sounding tube and, since it uses a 250V plate,
is relatively easy to power with readily available 115/230-115V
isolation transformers operated in reverse. And heater power is .76A
vs the 6DW5s 1.2A, which isn't trivial when running 4 of them.

I did a guitar amp with those and kind of like them. They also come in
a 45V heater version, the 45B5. I did a little stereo SE with those
and a 20EZ7 (20V 12AX7) with series heater string off a single
isolation transformer, so no filament transformer.

[John L Stewart]

'Alejandro Lieber[_2_ Wrote:
> ;952946']Why is it that the 6DW5 is not used any longer in PP audio

>>>>>>>>>>>>>>>>>>>>>>....

The schematic reminds me a lot of some very hard driven output sections
used in guitar amplifiers. But I guess the amp manufacturer had
reliablity data to support the somewhat extreme operating conditions.

The screen regulator does not use a stable reference, such as an 0A2 or
0B2. Rather the screen supply is hooked up to the -ve bias supply, which
does make a lot of sense here.

The 6DW5 specs look a lot like the 6W6 family & by extension the
25/35/50L6 group. I've found all those work well in audio, both SE & PP.
But not a good choice for the extreme voltages in the Bogen here.

Opinions only, John


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--
John L Stewart

[Alejandro Lieber]

flipper wrote:
> As for 'today' it's probably because people tend to copy what was
> common or 'popular' and that's not a bad starting place since there
> was probably some good reason why it was. The 6DW5 datasheet also
> doesn't give any audio amp numbers so DIYers don't have an 'easy' spec
> to go by.
>
> As for 'back then' your comparison doesn't hold because the 6DW5
> wasn't less expensive than the 6BQ5 and my 1961 RCA price sheet lists
> it as $3.20 vs $2.25, or 42% more expensive. Second, it needs a lower,
> regulated, screen and, in the Bogen, that sucks up the cost of a 6CM7
> regulator.
>
> The Bogen is also operating them at 435V, when Design Max specs 330V,
> and Class B which, assuming one doesn't mind Class B, requires the
> added complexity of fixed bias.

http://lieber.com.ar/6DW5.png

>
> In short, it isn't at all clear that's 'better' than a pair of 6L6GCs,
> and a plain ole simple B+ power supply, which could go up to 55 Watts
> Class AB or around 30 Watts Class AB UL for not much more tube cost
> (saving the 6CM7, alone, pays for the cost of one pair over the 6DW5).
>
> At any rate, a plain ole 6BQ5 PP amp would have certainly been less
> expensive not only in tube cost but the heater and B+power supplies
> and OPTs. Plus, 17/15 Watts is only 3 dB less than 30 Watts which,
> from a practical standpoint, doesn't really make all that much of a
> difference so the cost benefit ratio definitely favors the 6BQ5, which
> is probably why they were pretty common.
>
> Now, another 'not seen very often today' tube is the 6CW5, which can
> do 25 Watts 'in spec' Class AB, but it also takes a lower screen
> supply. But it's a good sounding tube and, since it uses a 250V plate,
> is relatively easy to power with readily available 115/230-115V
> isolation transformers operated in reverse. And heater power is .76A
> vs the 6DW5s 1.2A, which isn't trivial when running 4 of them.
>
> I did a guitar amp with those and kind of like them. They also come in
> a 45V heater version, the 45B5. I did a little stereo SE with those
> and a 20EZ7 (20V 12AX7) with series heater string off a single
> isolation transformer, so no filament transformer.

[Alejandro Lieber]

Alejandro Lieber wrote:
> flipper wrote:
>> As for 'today' it's probably because people tend to copy what was
>> common or 'popular' and that's not a bad starting place since there
>> was probably some good reason why it was. The 6DW5 datasheet also
>> doesn't give any audio amp numbers so DIYers don't have an 'easy' spec
>> to go by.
>>
>> As for 'back then' your comparison doesn't hold because the 6DW5
>> wasn't less expensive than the 6BQ5 and my 1961 RCA price sheet lists
>> it as $3.20 vs $2.25, or 42% more expensive. Second, it needs a lower,
>> regulated, screen and, in the Bogen, that sucks up the cost of a 6CM7
>> regulator.
>>
>> The Bogen is also operating them at 435V, when Design Max specs 330V,
>> and Class B which, assuming one doesn't mind Class B, requires the
>> added complexity of fixed bias.
>
> http://lieber.com.ar/6DW5.png

There are two errors in Bogen's DB230 schematics......
R105 should be 100 ohms, not 220k ohms.
R107 should be 220K ohms, not 100 ohms.

[Roger Jones]

On Feb 14, 8:34 pm, Alejandro Lieber <inva...@not-for-mail.invalid>
wrote:

On the topic of "minority audio tubes", I have a KNIGHT brand
amplifier for sale on eBay that uses a pair of 6CZ5's. These are 9-
pin glass, about the same size as the 6BQ5. In this amplifier they
run at a very high B+, over 437 V B+ at only 110 VAC mains input. In
one of the pictures at
http://www.ebay.ca/itm/KNIGHT-integrated-tube-amplifier-working-/150758233659
I show the DMM reading this on the bench test. The RCA tube manual
suggests 350 VDC on the plate as a maximum, 285 VDC on the screen.
Tube is listed as a TV vertical deflection amplifier and a TV audio o/
p stage (SE). In P-P with 7500 ohms plate-to-plate, over 20 watts
output is available (I got that wrong in the advert as I estimated
only 12-15 watts.)
Looks like a useful tube.
Cheers,
Roger

[flipper]

On Thu, 16 Feb 2012 11:24:13 +0000 (UTC), Alejandro Lieber
<inv...@not-for-mail.invalid> wrote:

>Alejandro Lieber wrote:
>> flipper wrote:
>>> As for 'today' it's probably because people tend to copy what was
>>> common or 'popular' and that's not a bad starting place since there
>>> was probably some good reason why it was. The 6DW5 datasheet also
>>> doesn't give any audio amp numbers so DIYers don't have an 'easy' spec
>>> to go by.
>>>
>>> As for 'back then' your comparison doesn't hold because the 6DW5
>>> wasn't less expensive than the 6BQ5 and my 1961 RCA price sheet lists
>>> it as $3.20 vs $2.25, or 42% more expensive. Second, it needs a lower,
>>> regulated, screen and, in the Bogen, that sucks up the cost of a 6CM7
>>> regulator.
>>>
>>> The Bogen is also operating them at 435V, when Design Max specs 330V,
>>> and Class B which, assuming one doesn't mind Class B, requires the
>>> added complexity of fixed bias.
>>
>> http://lieber.com.ar/6DW5.png
>
>There are two errors in Bogen's DB230 schematics......
>R105 should be 100 ohms, not 220k ohms.
>R107 should be 220K ohms, not 100 ohms.

Yep. Looks like somewhere in the documentation process R107 and R105
got transposed.