Good tube combination for Priboi amp?

[soundbrigade]

Sitting and basting a Regency corset, I let my thought wander off, far away from this nice project (that even will give me a few bucks).

I have a few "hard" projects I have to deal with and some I want to take care of. One of these is the infamous Priboi amp standing under my bed.
Many years ago I modified the original 50W PP-amp to a 12W quasi-triode class-A amp. Now I feel it's time to reverse that process, but as the 6R3S is a rather unreliable tube I thought that I could use either something BIGGER or a bunch of paralelled tubes.
I have a pair of EL156 and a pair of KT120 (need two more of these), and I can get two quartetts of 6L6 (Russian 6P3S) for very little money.


I picked up the following data för the OP transformer:

primary Rdc 87R
pry inductance 9,3H
measured a-a


secondary Rdc
0R8 for 4R winding
1R1 for entire winding (8R)

voltage ratio 18,4:1 ( measured full pry to full sec (8R tap and gnd tap)) , which means that Raa=2K7

[kheper]

I have a pair of EL156 and a pair of KT120 (need two more of these), and I can get two quartetts of 6L6 (Russian 6P3S) for very little money.

I picked up the following data för the OP transformer:

primary Rdc 87R
pry inductance 9,3H
measured a-a

secondary Rdc
0R8 for 4R winding
1R1 for entire winding (8R)

voltage ratio 18,4:1 ( measured full pry to full sec (8R tap and gnd tap)) , which means that Raa=2K7

If you could get another pair of EL156s, you could make a nice, unique amp. 2.7K Raa is a bit low, but if you have a 4ohm tap and use 8ohm speakers on the 4ohm tap, it would double to 5.4K.

I'm thinking 500Vdc B+ will get you about 50W audio output.

Does the transformer have a screen tap?

[azazello]

Magnus, I advise You stop build amplifiers with output transformers.
If You listen OTL, You never go back to all made Yours till now, like me....I don't listen my SE 300B, SE 2A3. You have very good hornes with Sonido with very good sensitivity, What You will do with PP - 50 watts. OTL is exotic and a level
higher in sounding, with very deep scene, very power bass, very big dynamics. Every expensive OTr. press sound in LF, scene and doesn't compare with OTL.

[soundbrigade]

Remember they're PPs.

Azazello: have too many transformed projects to start, before starting a new one.


Joe Stroud: Or did you mean another pair for second channel??

[kheper]

Remember they're PPs.

Azazello: have too many transformed projects to start, before starting a new one.


Joe Stroud: Or did you mean another pair for second channel??

Yes, for the second channel. EL156s are 50W tubes. They were used to produce 130W audio power in PP mode in old amps.

[soundbrigade]

But running them pretty conservatively will propably give me some 50W good sounding Watts, you mean.

The original PSU had a 240V and a 480V tap as well as taps for bias and 6,3 and 12,6V heaters.

[kheper]

But running them pretty conservatively will propably give me some 50W good sounding Watts, you mean.

The original PSU had a 240V and a 480V tap as well as taps for bias and 6,3 and 12,6V heaters.

Well, the max plate dissipation of the EL156 is 50W. The max audio power is ~130W in PP mode. At 500Vdc, I think you will yield about 50W audio power. At 60ma bias per tube, they will live a long time, unstressed.

500V * .060A = 30W

[kheper]

50 Watt EL156 PP triode mode:

[soundbrigade]

I have seen that one, but haven't had the guts to try it out. I am slightly allergic to the many trimmers, but they are propably no big issue.


The magazin Elektor Electronics published this one in 2005. It's rated 90W.


Schematic

[kheper]

I have seen that one, but haven't had the guts to try it out. I am slightly allergic to the many trimmers, but they are propably no big issue.


The magazin Elektor Electronics published this one in 2005. It's rated 90W.


Schematic

The trimmer used in the B+ supply can be replaced by a resistor. It seems to be for accommodating the 450-500 voltage range.

In your schematic, if you removed the power supply from the screens and ran in triode mode, you would get ~45W output wattage.

[soundbrigade]

Have gotten price for EL156 - around 50 EUR each.

Just another shot in the dark - 807!! I have understood that 807 is, even very much like 6L6 a pretty powerful little f*cker ...

I was thinking of the EL509 PP amp described in Rozenblit's Audio Reality. It uses a Hammond 1640T 1,9K transformer and I guess the Proboi iron will work fine here.

[burnedfingers]

I have seen that one, but haven't had the guts to try it out. I am slightly allergic to the many trimmers, but they are propably no big issue.


The magazin Elektor Electronics published this one in 2005. It's rated 90W.


Schematic

I am unable to bring up the schematic

[DeathRex]

Magnus, I advise You stop build amplifiers with output transformers.
If You listen OTL, You never go back to all made Yours till now, like me....I don't listen my SE 300B, SE 2A3. You have very good hornes with Sonido with very good sensitivity, What You will do with PP - 50 watts. OTL is exotic and a level
higher in sounding, with very deep scene, very power bass, very big dynamics. Every expensive OTr. press sound in LF, scene and doesn't compare with OTL.

You have a schematic?

[azazello]

Magnus, I advise You stop build amplifiers with output transformers.
If You listen OTL, You never go back to all made Yours till now, like me....I don't listen my SE 300B, SE 2A3. You have very good hornes with Sonido with very good sensitivity, What You will do with PP - 50 watts. OTL is exotic and a level
higher in sounding, with very deep scene, very power bass, very big dynamics. Every expensive OTr. press sound in LF, scene and doesn't compare with OTL.

You have a schematic?

http://www.diytube.com/phpBB2/viewtopic ... 3&start=15
Before phase splitter I put preampl. 1/2PCC88. I took +U from phase splitter after 3 kohm and 220 uF / minus to ground/. R plate - 20 kohm, Rcathode- 390 ohm, Rgrid- 470 kohm. Input potentiometer-2,2 kohm. In Your case all resistors will be approximately.
Current plate every 1/2 6AS7 - 70 ma. -Ubias about 90 V.
U under 820 + 820 ohm is 0 /no more 100 mV/, because currents upper and down shoulders in different direction
must be the sames, for avoid U under speakers. You can connect fast fuss 300-500 ma to save speakers and voltmeter. In the begin there is some U, after few minutes U must be min. and You can connect speakers.
Sound will be cool and awesome! /The best output transformer is missing!/