I have a OPT (10watts) for a 7591 PP that id like to use in a 6l6 PP with a 12ax7 feeding them, anything in the works, proven with that layout?
hey-Hey!!!,
I'd avoid the 12AX7 if I could( and I have certainly managed to ). A 7591 OPT is likely to be ~6kOhm plate-to-plate so it will work well with a wide variety of 6L6 operating points. its 10W capacity is about half what a pair can deliver even in Class A though.
Examine Eli Duttman's 'El-Cheapo' and adjust the front end stuff to live comfortably with 12AX7 operating points( like 100k plate loads and 2-3mA CCS setting ).
cheers,
Douglas
I'd avoid the 12AX7 if I could( and I have certainly managed to ). A 7591 OPT is likely to be ~6kOhm plate-to-plate so it will work well with a wide variety of 6L6 operating points. its 10W capacity is about half what a pair can deliver even in Class A though.
Examine Eli Duttman's 'El-Cheapo' and adjust the front end stuff to live comfortably with 12AX7 operating points( like 100k plate loads and 2-3mA CCS setting ).
cheers,
Douglas
Hmm, avoid the 12ax7 eh?
the 10w figure is it's half rate, it's full rating is 6.6k pri CT, with a 20w 100% duty cycle, I just like to baby my tubes.
the 10w figure is it's half rate, it's full rating is 6.6k pri CT, with a 20w 100% duty cycle, I just like to baby my tubes.
Dude,
You use the same O/P "iron" with 7591s and 6L6s, assuming power handling is adequate. Your trafos will work with triode wired 6L6s. NOS metal envelope tubes, with their 19 W. dissipation, which is the same as the 7591, are sufficient. What's the objection to the 7591? The current production EH 7591 is quite good. Remember, the 7591 is as easy to drive as an EL84; not so the 6L6. The 12AT7 based small signal circuitry in "El Cheapo" works well with 7591s, but it lacks the gain needed with 6L6 family tubes. I suggest a Mullard style circuit in combination with 6L6s. The H/K Cit, 5 is a good example to start with. Use an ECC99, instead of a 6CG7, as the LTP and you have high gm types everywhere in the small signal circuitry.
Why no 'X7? High RP and low gm make it a wretched driver. 🙁 Unfortunately, the type can't fight its way out of a wet paper bag. Also, in circuits with GNFB loops, high transconductance small signal circuitry provides resistance to slew limiting associated with the HF error correction signal.
You use the same O/P "iron" with 7591s and 6L6s, assuming power handling is adequate. Your trafos will work with triode wired 6L6s. NOS metal envelope tubes, with their 19 W. dissipation, which is the same as the 7591, are sufficient. What's the objection to the 7591? The current production EH 7591 is quite good. Remember, the 7591 is as easy to drive as an EL84; not so the 6L6. The 12AT7 based small signal circuitry in "El Cheapo" works well with 7591s, but it lacks the gain needed with 6L6 family tubes. I suggest a Mullard style circuit in combination with 6L6s. The H/K Cit, 5 is a good example to start with. Use an ECC99, instead of a 6CG7, as the LTP and you have high gm types everywhere in the small signal circuitry.
Why no 'X7? High RP and low gm make it a wretched driver. 🙁 Unfortunately, the type can't fight its way out of a wet paper bag. Also, in circuits with GNFB loops, high transconductance small signal circuitry provides resistance to slew limiting associated with the HF error correction signal.
Id like to find a nice P-P 7591 schematic, but I was told the 6l6 conversion was quite common a while back, when the 7591 was out of production for a while.
Also, the iron I have for this 7591 is a non-ct 175vac with no caps, and with 1500uf of electrolytic through a modern (overkill) 25amp bridge rectifier, I get 248vdc, though I keep seeing people say the 7591 was quite common @ 500vdc and there about.
That 7591 power trafo is intended to be used with a Greinacher ("full wave") doubler supply. That's exactly what you'll find in the H/K Cit. 5. 😉 Under load, the B+ rail will come in at approx. 450 V. A pair of 600 PIV Schottky diodes would give you "noise free" operation.
Just use it from the Loudness control on (6BL8/6*8 Gain stage, Phase splitter, and outputs).
The 0.047uF cap and 68R resistor were probably associated with the particular OPT and could be dropped or values determined with a square wave test.
The 0.047uF cap and 68R resistor were probably associated with the particular OPT and could be dropped or values determined with a square wave test.
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And yet, many vintage amps used them.😕
That's exactly how they sound too.😀
jeff
Dude,
If you are willing to use 7591s, the 12AT7 based small signal circuitry in "El Cheapo" will serve you well. You could use the same low cost B- setup too.
If you are willing to use 7591s, the 12AT7 based small signal circuitry in "El Cheapo" will serve you well. You could use the same low cost B- setup too.
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