Pentode CCS for parafeed SEP??

[aletheian]

I am currently building up a single ended EL34 amp, and I am soooooo ******** bored waiting for the transformers to com ein that it has developed into quite a project.

Originally I was going for minimalism, with a small CLCRC oil cap supply, but I got bored and wired up a mosfet regulator... then I added some other bells and whistles... and NOW I have an Amperex EF184 just BEGGING to be hooked up as a CCS.

So my question is, has anyone done it and what would the caveats be? I have done pentode CCS in preamp sections, but always with triodes. What should I be mindful of if I convert this thing to parafeed and load up the plate of the EL34 with the EF184?

Thanx.

[mach1]

You can't use a CCS with pentode - they will both fight each other and the tube won't bias up properly.

If you wire the pentode in triode mode it's fine.

regards

[aletheian]

CRUD! That's right... i remember now why I have not done it.

OK, how about a solid state gyrator circuit loading the plate of the EL34?

[Shoog]

Why are you fixed on using the EL34 as a pentode. Do you really need the extra watts. It will sound better in triode mode.

I have built a SEPP amp using 807's as the output tubes. The CCS load is made from a TT21(KT88 with top cap). I tried one of Gary Pimms Pentode CCS's but the voltage across the TT21 collapsed. I had voltage to spare so I dropped about a 100V between the CCS and the 807 in order to stiffen the CCS. I took the output from the top of the 807 rsather than the MU stage option.I sent it through a 1000V 4uf Paper in Oil cap and it drives a 6V mains torodial (about 120VA). Sounds really sweet and a very simple circuit overall.
This configuration hums very little with only minimal power supply filtering.

Shoog

[aletheian]

Originally posted by Shoog
Why are you fixed on using the EL34 as a pentode. Do you really need the extra watts. It will sound better in triode mode.

I have built a SEPP amp using 807's as the output tubes. The CCS load is made from a TT21(KT88 with top cap). I tried one of Gary Pimms Pentode CCS's but the voltage across the TT21 collapsed. I had voltage to spare so I dropped about a 100V between the CCS and the 807 in order to stiffen the CCS. I took the output from the top of the 807 rsather than the MU stage option.I sent it through a 1000V 4uf Paper in Oil cap and it drives a 6V mains torodial (about 120VA). Sounds really sweet and a very simple circuit overall.
This configuration hums very little with only minimal power supply filtering.

Shoog

Yeah, I am pretty set on pentide... that was the whole point of the thing actually, to try out a SE pentode amp. I wired up a gyrator circuit last night out of a mosfet, a cap and a resistor. I'm going to give it a try when my parts come in unless anyone has a warning for me against the idea. I have never uilt one before, so I'll have to see what happens. Worst case scenerio=blown mosfet, and then i am only out about $1.

[Tweeker]

Why are you fixed on using the EL34 as a pentode. Do you really need the extra watts. It will sound better in triode mode.

I suspect hes not planning to use this amp for hifi, he might not object to a little distortion. I wouldnt be surprised if its way overdriven to boot.

[aletheian]

Originally posted by Tweeker


I suspect hes not planning to use this amp for hifi, he might not object to a little distortion. I wouldnt be surprised if its way overdriven to boot.

DANG! Did the hair and guitar give it away? THAT'S IT, I'm changing my avatar to a Westinghouse 300b! They are sexier than I am anyway.

But honestly, in terms of output stages, your average instrument amps and hi-fi amps are not too dissimilar in general design terms: parafeed is parafeed, SRPP is SRPP, AB1 is AB1. They just vary in freq response and distortion requirements... (and component quality.
I usually get run out of town as a heretic by the guitar amp guys for my hi-fi leanings and the use of SS regulators and oil caps though.

Consequently, I have built up triode instrument amps and they sounded too spongy... gotta be a pentode for me.... or UL. but seriously, if anyone has tried a gyrator on the plate of a pentode in parafeed, I'd be thrilled to know the results.

[Shoog]

There have been some good threads on this very subject recently which have only just died down. There are more knowlegable contributers to those than me. Go back a page or two on the Tube listings and you will find them. I suspect you will need to consider plate chokes - which brings you back into the big bucks again.

Good luck.

Shoog