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Old 6th May 2007, 07:26 AM   #21
Klimon is offline Klimon  Belgium
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But ofcourse the components of a notch are arranged in a different fashion.... (still rambling).... I'll have to take the high µ lead...

Simon
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Old 5th June 2007, 05:51 AM   #22
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Quote:
I would like to build my first pp; a 6as7 circuit to suit the tubes and opts I already have
You might like to check out http://www.wimdehaan.nl/tubeamps/6as7g/index.html for a PP design using the 6AS7G yielding 10W at 0.26% distortion with only 8dB feedback. Design uses a common 3K4 output transformer.

Wim
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Old 5th June 2007, 12:41 PM   #23
jayme is offline jayme  United States
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Quote:
Originally posted by wimdehaan


You might like to check out http://www.wimdehaan.nl/tubeamps/6as7g/index.html for a PP design using the 6AS7G yielding 10W at 0.26% distortion with only 8dB feedback. Design uses a common 3K4 output transformer.

Wim
How is the bass with only 100uF caps in the cathode bypass on the 6as7?
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Old 6th June 2007, 03:03 AM   #24
jarthel is offline jarthel  Australia
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Default to wimdehaan

6as7 are known to have mismatched triodes.

is there a way to matched them in the circuit?

some designs I've seen (e.g. andrea ciuffuli's pse EL34) uses separate bias for each of the triode.

also since there is no power supply schematic provided, can you tell me what did you use?

thank you.
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Old 6th June 2007, 03:22 AM   #25
jarthel is offline jarthel  Australia
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Quote:
Originally posted by wimdehaan


You might like to check out http://www.wimdehaan.nl/tubeamps/6as7g/index.html for a PP design using the 6AS7G yielding 10W at 0.26% distortion with only 8dB feedback. Design uses a common 3K4 output transformer.

Wim
Hi wim.
some questions in regards to your design.

1. 6as7 are known to have mismatched triodes. is there a way to matched them in the circuit? some designs I've seen (e.g. andrea ciuffuli's pse EL34) uses separate bias for each of the triode.

2. Also since there is no power supply schematic provided, can you tell me what did you use?

3. If I decided to double the number of output triodes, what changes are involved?

4. Where is the +LS and -LS connected? are they connected to the speakers? Is the +LS that is connected to the white lead the 8hm output? if I connect it to the other output lead, how do I calculate R28?

5. is there any advantage to using lower voltage on V1 to V4 so I do not have to use high value resistance to drop the voltage to required levels? I know that the drawback is the possible requirement of another secondary to provide the lower voltage.

6. since you are using a negative supply for the CCS, did you connect the ground of the -12 supply to the B+ ground?

thank you.

thank you the help
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Old 6th June 2007, 06:03 AM   #26
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Quote:
Originally posted by jarthel

Hi wim. some questions in regards to your 6AS7G design.
Answer 1: yes, many 6AS7 are really mismatched, even RCA types. Using P3 you can adjust the balance. I am using a small 100uA-0-100uA meter (needle in the middle) for optical adjust for balance, this works good. BTW on Ebay there is a german perosn who sells russian 6AS7 as matched pairs for not too much. I have a few, but never tried them. I have some RCA's doing the job.

Answer 2: I did update the website, the PSU is now available as PDF file. I am using a straightforward design using 2 chokes as can been seen in the photos. Important thing to know is that the cathode of the E88CC is not related to ground but to +190V, so this heater has to be floating from ground, I am using a 1uF film cap to ground the heater.

Answer 3: the primary impedance of the output transformer, for 4 tubes in PP 1,9K would be an option. Mine is using 2 in PP, and it is loud enough. I would not recommend 4 tubes.

Answer 4: LS is loudspeaker. This transformer has 4, 8 and 16 ohm out (and 2 ohm I believe), I am using the 4 ohm output. R28 is a divider with R5 (approx. Uo/Ui= R5/ R+R9). 8 dB feedback I found is a good compromise in with and without feedback. I prefer without, but the 6AS7 needs some to make it measure okay. For R9 I use in the test setup an adjustable resistor and using a AC meter it is easily set for 8 or 10 or 12 dB FB.

Answer 5: V1 to V4 are very critical. The 6AS7G needs an enormous voltage to drive them. I believe it was 80 or 90V AC RMS (neg. bias voltage is -134V). Will check if you want to know for sure. It is a very insufficient tube and difficult to handle, in some design on some website they gave up because of no good overall results in distortion. I tried many driver tubes and the E88CC shows best overall result, according to many DIY people this tube doesn’t ‘sound’, I feel the same, but many people listened to this amp (of course including me) and they (and me) can’t ‘hear’ the E88CC. I am using the new made JJ Electronics.

Answer 6: Yes the ground of the CCS is connected to B+ ground, in this design I strictly use star-ground, so many ground wires in this amp.

BTW the CCS for the E88CC is essential without (so using a common resistor) specs are going badly the wrong way. Other clue, is the 150 ohm resistor in the output stage, if you have a distortion analyser you might like to check the behaviour of the 15 cents component ;-)

Wim
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Old 6th June 2007, 07:05 PM   #27
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The Russian 6H13C are softer and less detailed sounding than the RCA's. If feedback is employed I would quess there wouldn't be much in it. The 6H13C's look nicer though.

My 6080 amp got a good reception at a local meet at the weekend. The 6080's are not disappointing.

Shoog
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Old 7th June 2007, 07:53 AM   #28
jarthel is offline jarthel  Australia
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Quote:
Originally posted by wimdehaan

Answer 1: yes, many 6AS7 are really mismatched, even RCA types. Using P3 you can adjust the balance. I am using a small 100uA-0-100uA meter (needle in the middle) for optical adjust for balance, this works good. BTW on Ebay there is a german perosn who sells russian 6AS7 as matched pairs for not too much. I have a few, but never tried them. I have some RCA's doing the job.
so with the amp meter, how do you adjust it so they match? to make it balanced, does the needle have to be in the middle?

Quote:
Originally posted by wimdehaan

Answer 3: the primary impedance of the output transformer, for 4 tubes in PP 1,9K would be an option. Mine is using 2 in PP, and it is loud enough. I would not recommend 4 tubes.
is the impedance the only changes? How do I connect the extra tubes to the circuit? any chance of a new schematic/drawing?

Quote:
Originally posted by wimdehaan

Answer 5: V1 to V4 are very critical. The 6AS7G needs an enormous voltage to drive them. I believe it was 80 or 90V AC RMS (neg. bias voltage is -134V). Will check if you want to know for sure. It is a very insufficient tube and difficult to handle, in some design on some website they gave up because of no good overall results in distortion. I tried many driver tubes and the E88CC shows best overall result, according to many DIY people this tube doesn’t ‘sound’, I feel the same, but many people listened to this amp (of course including me) and they (and me) can’t ‘hear’ the E88CC. I am using the new made JJ Electronics.
I may have been unclear with my question.

Is there any advantage to having a separate B+ for the V1 to V4. So I have say a 195V supply and another 383V supply.

Quote:
Originally posted by wimdehaan

Answer 6: Yes the ground of the CCS is connected to B+ ground, in this design I strictly use star-ground, so many ground wires in this amp.
how about the negative supply? where is it ground connected? did you leave it "hanging"?

new question: what transistors did you use to make up the CCS?
thank you for the help
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Old 14th June 2007, 11:49 AM   #29
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Quote:
Originally posted by Jarthel

Answer 1: yes, many 6AS7 are really mismatched, even RCA types. Using P3 you can adjust the balance. I am using a small 100uA-0-100uA meter (needle in the middle) for optical adjust for balance, this works good. BTW on Ebay there is a german perosn who sells russian 6AS7 as matched pairs for not too much. I have a few, but never tried them. I have some RCA's doing the job.

so with the amp meter, how do you adjust it so they match? to make it balanced, does the needle have to be in the middle?
Yes, when the meter is in the middle both sections conduct the same current.

Quote:
Originally posted by Jarthel

Answer 3: the primary impedance of the output transformer, for 4 tubes in PP 1,9K would be an option. Mine is using 2 in PP, and it is loud enough. I would not recommend 4 tubes.

is the impedance the only changes? How do I connect the extra tubes to the circuit? any chance of a new schematic/drawing?
I would not do so, driver stage will be stressed. In my home the 2 tubes makes a lot of 'noise', it's loud enough.

Quote:
Originally posted by Jarthel

Answer 5: V1 to V4 are very critical. The 6AS7G needs an enormous voltage to drive them. I believe it was 80 or 90V AC RMS (neg. bias voltage is -134V). Will check if you want to know for sure. It is a very insufficient tube and difficult to handle, in some design on some website they gave up because of no good overall results in distortion. I tried many driver tubes and the E88CC shows best overall result, according to many DIY people this tube doesn’t ‘sound’, I feel the same, but many people listened to this amp (of course including me) and they (and me) can’t ‘hear’ the E88CC. I am using the new made JJ Electronics.

I may have been unclear with my question.

Is there any advantage to having a separate B+ for the V1 to V4. So I have say a 195V supply and another 383V supply.
In a way not. If you look at the PSU you will see, that the driver stage has it's own RC network.

Quote:
Originally posted by Jarthel

Answer 6: Yes the ground of the CCS is connected to B+ ground, in this design I strictly use star-ground, so many ground wires in this amp.

how about the negative supply? where is it ground connected? did you leave it "hanging"?
To the central earth.

Quote:
Originally posted by Jarthel

new question: what transistors did you use to make up the CCS?
thank you for the help
I am using the BC550B.

Wim
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Old 14th June 2007, 06:11 PM   #30
mus is offline mus  Canada
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Hi All,
I'm quite interested about this project too. Also I found an unusual schematic http://www.dhtrob.com/schemas/afbeeldingen/6as7pp.gif which the plates of the driver stage are inverted connected to the UL-taps of the OPT's. Is there any advantage or disadvantage? What would be the output wattage? Thanks.

mus
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