The Amp Garage

bumping this query.

Anyone able to take an educated guess about how it's done?

just remembered there was also a thread about the feasibility of a variable zener approach similar to Paul Ruby's fix for inclusion in a scaled/vvr'd 18 watt. I believe the outcome was that the modder ended up with testing a succession of zeners and settling on a low value zener which suited the who...

unsurprisingly, there is a lot of info on the 18 watt site about taming the fizz associated with heavily overdriven el84s. I can sympathise with the poster's comments about the swirly fizz at low voltages. I tried all the suggested fixes for dealing with fizz in the 18 watt circuit, including the co...

presumably a smaller fuse in the mains supply too

Steve at valvepower appears to have expanded his transformer line. Follow the link to ebay from the valvepower web page.

so, am I correct in assuming I can put the speaker on the next lower tap for these and be reasonably in the ballpark? i.e a typical transformer for an el84 18w amp.

has anyone tried / seen these in a push pull cathode-biased output stage?
I'm trying to get some advice about bias resistor and transformer requirements.

Thanks

I was wondering whether it might be another option to consider by those trying to eliminate fizz from their vvr'd el84 power amps

I would be interested to know whether anyone has experimented with hotter than typical bias settings in cathode biased vvr/scaled amps. I'm making the assumption that if you always run your amp at home/practice levels, then the plate voltage will be nowhere near high enough to cause the tube to reac...

I'm sure there was a design fault documented for these. Something like the bias supply being the wrong side of a fuse ?? i.e potential for the power tubes to lose bias in an unrelated fault condition. Might be worth checking into and budgeting for a modification.

if you're preferring UK based, Steve at Valvepower has some decent transformers for 18 watt el84 builds

Lindz, thanks for the additional description. Somehow, I need to school myself on these mechanisms a little more. The ultimate 18 watt scaling solution may be within our grasp!

Any chance of some clips?

So, if I'm following correctly, you've applied a zener that is not within 2 volts of the bias on a fixed bias AND a cathode biased amp, both of which have a Hall vvr fitted. The amps sound normal throughout the vvr range? How low are you going on the vvr? I second the point about hoping we can get a...

After trying different grid resistor values, zobel filter, and higher value el84 cathode resistor bypass cap, the only way I removed the 'vvr dialled down fizzies' was to disconnect the el84 cathode resistor bypass cap altogether. The caveat here is that my amp is permanently run at low vvr settings...

the rebel has 2x el84 and 2x 6v6 , not one of each sharing the push- pull