My low watts projects

[TomMcNally]

I just got a lot of 7 GE used/matched/tested for $ 2.65 each on eBay.
Time to build something!

[TerrySmith]

I also agree, Stan at ESRC is a good feller. His tube prices are about the best around, most of the time better than what you find e-pay.

[EWBrown]

I decided to stay with 6AV5GAs, damn the torpedoes, full speed ahead

I wired up the output stages, using the Transcendar 10W, 3K SE OPTs, and 750 ohm 25W "heatsink" type dale cathode resistors.

With 400V B+, the test 6AV5GAs were dissipating about 25 Watts combined plate and G2. Even though these tubes can take a lickin' and keep on tickin' I decided to throttle things back a bot, added an extra C (47 uF / 450V) and R (333 ohms, 30W, three 1K, 10W WW resistors in parallel), before the choke..

That dropped the B+ to 365VDC, before the choke, and 350VDC to the OPT B+ connections.. Instead of 75 to 80 mA plate current, I now get 66 - 68 mA, and a V P-K of about 280V so I'm down to around 18-29W PD, which is closer to reality. Before I throtled it back, I ran tests about three dozen 6AV5GAs and culled out the four weakest ones, and one which oscillated uncontrollably.

I even subjected half a dozen 6AV5GTs to this treatment, and they didn't blow up.either.

I made up another SS 6AX5GT replacement, this time with 50 ohms in series with each uF4007 ,and I added another diode, LED and 680 ohm resistor across 2 and 7 to get a red "filament glow". I tried that out in the "blue plate special" GSG and get the same B+ voltages, though with a slightly lower cathode current, because of its approx 800 ohm vs. 750 ohm RK's.

With this combination, it is noticeably more powerful, better bass, and clear highs, I have run it this way for a few hours, with no ill effects on the tubes, and the PA774 just gets slightly warm. It now has 1.2A less loading on one of the two filament windings, so that saves about 7.5 VA's in the process. It definitely has a much better "Ka-Whump" factor, now

Next, on Thursday or Friday, I'll build up the new amp's 12AT7 driver stages, with SRPP.

And just for ha- ha's, I have also started ANOTHER G*S*G , the chassis is drilled and punched for the PC board, next will be the other two tube socket holes, and mounting holes for the iron, etc. Next year

I'm still deciding whether to use 6B4Gs, 2A3s or 6AV5GAs, or

Photos coming RSN

/ed B in NC

[Quad]

Hmmm - a couple of interesting possibilities here -

* Make the GSG switchable to use 6B4Gs or 6AV5GAs.
Pins 1 and 8 are NC on the 6B4G. So the 470ohm resistor
on the socket shouldn't affect the 6B4G. Not using UL mode
should simplify this mod a bit.
Is it possible to do with just a DPDT switch per side?

* More drastic - rewire the GSG board as a stereo SPUD
using a pair of 6EM7 (eliminating the 6SL7).

[azazello]

Next my two stages ampl. SE JJ 300B & 6E5P & OT Hammond 125 FSE - 90 ma, chase Hammond.
Two electr. chock filtering, fixed bias, caps - Auricap, ELNA Cerafine, Phillps, Rubycon.

http://picasaweb.google.com/azazello52/ ... 4050970514
http://picasaweb.google.com/azazello52/ ... 2897531442

[Ty_Bower]

What's the minimum voltage rating of the cathode bypass caps (C2 and C4) in this amp? Is it bad to go too high on the voltage rating? Looking in my box of parts, I've got either a tiny Elna "audio" cap (47uF/6.3v) or a Nichicon "premium audio" (47uF/25v) available for the triode gain stage. For the finals, I've got either a Nichicon "audio" (330uF/35v) or a Nichicon "premium audio" (220uF/50v).

I guessing that for the parts I've got on hand, any of them would be fine. I'll probably just use the Nichicon KZ caps for everything.

[EWBrown]

The voltage ratings of the cathode bypass caps isn't too critical, as long as it is abve the actual voltages encountered in use, in this circuit is only a couple of volts maximum. I generally have been using 47 uF /10V, 47 uF / 16V and 47 uF / 25V only because I have a large quantity of these values.

For the Pentode bypass cap, which normally receives 13 to 16V across it, anything from 25V upwards is fine, I generally use 35V rated caps for this voltage range, just as with EL84s. It is not good to use a 16V rated cap at these voltages, as it would have a fairly short lifetime, failure isn't a matter of "if", it's a matter of "when". .

At a minimum I will use a cap which has 20 to 25% higher voltage rating than the maximum expected cathode voltage, and higher volt ratings won't hurt. No real sense in using a 450V cap for a 24V cathode voltage, but if it's the only thing I have available at the time, I'll go ahead and use it temporarily , at least until I can replace it with something of a safe voltage rating.

/ed B

[azazello]

https://picasaweb.google.com/azazello52 ... 9815226946
PP-variant Leibovitz- 6П1П /6V6, 6AQ5, 6П6С/ & ECC81 & OT Hammond 125E....2 x 6-7 Wts

[TomMcNally]

https://picasaweb.google.com/azazello52/Amplifiers#5572498189815226946
PP-Leibovitz- 6П1П /6V6, 6AQ5, 6П6С/ & ECC81 & OT Hammond 125E....2 x 6-7 Wts

Wow ... I just looked at all 124 of your pictures, lots of cool amps!

... tom

[azazello]

Thanks! Now I have more of 124 future ideas......

[azazello]

Next my two stages ampl. SE JJ 300B & 6E5P & OT Hammond 125 FSE - 90 ma, chase Hammond.
Two electr. chock filtering, fixed bias, caps - Auricap, ELNA Cerafine, Phillps, Rubycon.

http://picasaweb.google.com/azazello52/ ... 4050970514
http://picasaweb.google.com/azazello52/ ... 2897531442

Sorry for doubling, but BTW...... This is first ampl. in the word with great driver Russian tube 6E5P!
This is first 300B's new sound!

[azazello]

My "pocket" SE with audiophile tubes 6Ф3П /ECL82/ with strong bass and clear sound.
https://picasaweb.google.com/azazello52 ... 3544989442

[EWBrown]

Nice one! You have the same type of Russian made (Svetlana) tubes that I used.

I made a small SEP like yours and a larger paralleled SEP version with 2 6BM8 / 6Ф3П / ECL82 in each channel, and 3.5K UL OPTs. These are posted elsewhere.

/ed B

[soundbrigade]

I have a strange feeling I'm into a hectic ADHD-period. First I started out with an 2C39A-amp, then I stumbled upon some wooden boxes and drilled some holes to house a pair of 6V6-PP monoblocks and nopw I am assembling a GroundedGrid preamp. And when you, Azazello, mentioned a pocket size amp I came to think about the 6AQ5-Se and the piensize amps I am/was assembling.

[azazello]

My listening room. Hornes with Fostex FE 206E
Fro left to right on the shelf:
SE 6Ф3П, SE 2A3 RCA, OTL 6AS7, EL11 Telefunken, PP 6П3С - variant Leibowitz.
On the floor: PP 6005 - variant Leibowitz, SE 300B JJ, SE 6С4С, SE EL11 Tungsram.
https://picasaweb.google.com/azazello52 ... 0015416338