JJ EF806 tried in a Bitsa 6V6er

[nickt]

Just got the chance to try out my new JJ EF806. The result so far - inconclusive.

Compared to the EH EF86 already in the amp the JJs were much less microphonic (but were still more ringy that I would like). The EH sounded best but that is in a currently flawed amp - so I don't think it counts.

The amp is basically an EF86 18watt with 6V6's in the output jammed into a weber 5C3 chassis with Zaphod's 22k tail resistor on the PI and various stoppers and limit resistors on the power tubes - in short - it doesn't know what it is!

Current problems are:
- woffy bass (possibly cause by lowish voltage on the 6V6's)
- input to wiper of volume pot - can't be good for EF86's - can it?
- tone circuit not installed yet - no caps!

On the good side both the EH and the JJ's have nice fat lead tones.

I'm going to continue sorting out the general amp problems. I'm pretty sure the biggest issue is the EF86 plate connected to the wiper of the volume control. This would mean the 86 sees varying impedance with volume change - is this as bad as it sounds?

I've currently got the 6v6's running 50 volts lower than available (5Y3 vs GZ34). I tried the GZ and the sound was better but the tubes were dissipating 18watts each!! So I need to rebias.

Anyway plenty of work to do.

Any ideas on de-woofing would be much appreciated.

[nickt]

Ok added the GZ34 and now have 415V on the 6V6s.

Upped the cathode resistor to 390R. With 28.5V across it I think that's 14W per tube which is probably too high - better get a 470R and try that. I'm assuming it will get me down to just under 12W.

Before upping the volts I swapped the leads on the Volume to the more normal input to top out to wiper - this fixed most of the woofyness. Heehaw!

I think I'd better scout around for appropriate preamp jolts. Upping the voltage has changed the sound significantly although I only got 3 secs of playing in before the resident females started complaining

More as it comes to hand...

[LooseChange]

Want more volts? Pop in a replacement SS recitifier or wire some in.

[nickt]

Want more volts? Pop in a replacement SS recitifier or wire some in.

Yeah, I could squeeze another 15-20V compared to the GZ34.

I think I'd better sort out the preamp volts first though. B4+ is about 350V at the moment which I think is a bit high for the 86 and the bias is right on max for the JJ 6V6s.

Funnily enough I've never had an amp with a tube rectifier before. Even my AC30 has diodes wired across the rectifier socket. I even think it was me who wired them in - 1974 is a bit of a dim memory these days!