Have a Unison Research Simply Two. This unit is auto biasing. Replaced the preamp tubes with NOS Amperex 12au7 - fantastic! Need to replace power tubes. Manufacturer says EL34/6CA7. Is a 6CA7-EL a true replacements? Several other EL34 have suffexs too. In another thread, someone used KT-77, a supposed drop in replacement for the EL34, but had a resistor(?) burn out. Should I be safe using any EL34-xx or 6CA7-xx tube?
Tube replacements/equivalents
- Thread starter Dclay1
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Not sure what a 6CA7-EL is but the EH biases hot. In my ST-70 it required modification of the bias circuit because with the pots at minimum, it was still too hot.
In the ST-70 I believe there is more top end compared to the Chinese 34s. The 34s sound warmer. How they would behave in your amp is anyone’s guess.
The EL34/6CA7 has a slightly different pin out than the KT77. In the KT77, the suppressor grid (g3) is connected internally to the cathode at pin 8 and pin 1 is open. For the EL34/6CA7, these two elements are NOT connected internally and the suppressor grid is tied to pin 1.
This should be kept in mind when designing a circuit where either tube is to be used.
This should be kept in mind when designing a circuit where either tube is to be used.
I expect that anything labeled as an EL-34 or 6CA7 would drop in. KT77's will drop in in many circuits with the above caveat. In a fixed bias set up you would have to re-bias. If by auto bias you mean cathode bias, you wouldn't. I worked on a Scott 272 that would take all of the above, but fixed bias had to be re-set. Best way is to check the data sheets for the tube vendor.
Thanks so much for responding! May have my terms incorrect. There are no pots to adjust bias on my amp. Emailed vendor, but they are in Italy....understand email response may not be a high priority now. The "manual" for the amp was written by a nonnative English speaker and is lacking any real info.
Here's an old AK thread that might be informative. If the Simply Italy amp is a pure evolution of the Simply Two, it is cathode bias (often referred to as 'automatic' bias). There seems to be periodic trouble with the cathode bias resistor overheating, particularly if higher-power KT77 tubes are used (consistent with your comment above on 'resistor burn out.' Sounds like you might want to stick with EL34/6CA7 tubes if this is also correct for the Simply Two.
Here's the link to the thread: https://audiokarma.org/forums/index...th-a-unison-research-simply-italy-amp.718452/
There's a schematic that might be helpful, depending on whether the Simply Italy amp is close to the design of the Simply Two.
The cathode bias resistor in question is labeled as R10 on this schematic (330 ohm 5W).
EDIT: the linked schematic is labeled as for the Simply Two amplifier. It looks to have been drawn by someone who examined the circuit and drew the schematic.
Good luck with it!
Dave
Here's the link to the thread: https://audiokarma.org/forums/index...th-a-unison-research-simply-italy-amp.718452/
There's a schematic that might be helpful, depending on whether the Simply Italy amp is close to the design of the Simply Two.
The cathode bias resistor in question is labeled as R10 on this schematic (330 ohm 5W).
EDIT: the linked schematic is labeled as for the Simply Two amplifier. It looks to have been drawn by someone who examined the circuit and drew the schematic.
Good luck with it!
Dave
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