el84 bias...How hot?

[Dave H]

No asymmetrical clipping for me. If it doesn't sound like an AC15 I'm not interested.

[Chuck H]

The CCS is a good idea. I'm more likely to approach it as I did because, well, it's a tube circuit! I like to romanticize that the flopping around of parameters are part of the mojo. But since the self split circuit is a goofy notion for guitar amps in the first place my sensibilities aren't offended by a silicooty addition. Mesa uses that idea for one of their phase splitter designs and it works quite well.

As to asymmetry, I think it's fine. Important in fact. But if you clip within a loop like the self split circuit the waveform can start looking weird. Like one side having a rounded bump on the clip and the other side having a rounded indent. I experimented with a circuit like that once and it didn't sound good. Looks pretty weird on a scope too.

[kg]

i've always been partial to the sound of this amp. http://ken-gilbert.com/images/tubes/schema.gif

sounds louder than the 10w would indicate, that's for sure. i guess KISS works after all.

[Chuck H]

Happy to have the input of a trusted voice on this. How does it sound clipping? And have you ever scoped it to see what the clipped wave form looks like?

[jazbo8]

i've always been partial to the sound of this amp. http://ken-gilbert.com/images/tubes/schema.gif

sounds louder than the 10w would indicate, that's for sure. i guess KISS works after all.

Ken's amp is a very different animal compared with the 15H, other than the self-split part - it uses IT coupling and EL34 triode-strapped. just saying...

[barfoden]

Hi Chuck thanks again for all the input...

Here is a link to the scheamtic of the amp,.,

http://www.ljudbojen.com/download/fi...df391fee05d1cd

On the OT it is listed that the primary is 10k, and you can see that the screen voltage is dropped by a 4.7K resistor. When my wall voltage is stable around 231V (Sweden) I get around 328V plate, 281V screen, 9.35V on the 91 ohm bias resistor, and a total current draw over the 200 ohm sag resistor of around 107mA.

Yesterday I tried the amp and the wall voltage was higher at 240V. All the voltages increased and the voltage drop over the bias resistor was ~9.49V and the plate dissipation (minus 10% screen) was around 15 watt and the clean headroom was gone..

The little brother amp (kustom defender 5h) which is a single ended amp has according to one schematic I have found (not sure if it original) shows a 280VAC/50mA rated PT, 5K OT, 220 ohm sag resistor, a 4.7K screen dropping resistor, and a bias setup which is a 270 ohm resistor bypassed with a 22µf bypass cap.

One guy measured a voltage drop of 11.36V over the 270 ohm resistor and a plate voltage of 348V. If I do the math.. I get 42mA combined cathode draw, if I deduct say 5mA for the screen this would get you 37mA plate current.. Then multiply with true plate voltage (348-11,36=336,6V) and you get around 12.5 watt.. Which sound like a decent dissipation for a class A EL84 amp.

My kustom 15h sits around 14.5W of idle plate dissipation.

[cyclone]

I build fixed bias push pull 6bq5 (amurican!) guitar heads. Plate voltage is at 378 vdc, screens at 365 or so. I get up to 21 watts with excellent tubes, russian, nos mullard or nos usa. I bias until the notch goes away, or by the cathode current method 21 ma. Or until I have 378 volts on plate. Same exact results, I can do three amps by three different methods and be within 2 ma cathode current on all of them. No problems long term.

If you get 25 watts clean out of a ygm3, your meter might need cal. Heres one at clean max out on a 200mhz techtronix scope. You won't see the crossover notch well or be able to tell that its flattening out the top of the waveform on a cheap scope. Its just starting to flatten in this pic, 8 ohm dummy load. Rms voltage on right, u guys know

This is before I put 1k screen resistors in, they were white hot with no resistor on them. Power output dropped a watt or two with screen resistors

[cyclone]

Sorry, attachment probs. the waveform that shows 9vrms is with the worn out JJ's that it came with. 12.96vrms is with 6p14p-ev's, supposedly a 7189a equiv. in my opinion, they ard no better than a standard 6bq5, same output when I 've tried them.

[cyclone]

Hi Chuck
Somehow, through my inability to conquer cel technology, I managed to reply to the middle of your thread. I put up a screenshot of a ygm 3 at max clean output, post 12, in case you missed it.

I also have an assortment of 7x 2 or 3 watt cathode resistors @ 130 ohms that have a cool metal heatsink that bolts to the chassis. They are out of hammond ao43 (2x6bq5) output sections and they range in resistance from 120 to 150 ohms. I'm not going to use them as I'm all fixed bias all the time, don't like the sluggishness of cathode bias, rather use screen compression. Pm me and i'll put them in the mail if u want them. No e of them looked like they were overheated or show signs of deterioration. I appreciate the help you've given me and the remark you made recently, which I resemble:

" I'm an obsessive, truth-pounding asshole that people eventually learn to dislike"

Damn, thats me to a T!

[Chuck H]

Ha ha! Wow! I remember saying that, BUT... I should have followed with: "Provided I'm not mistaken." It happens. Then I'm a pariah! It's pretty lame to be sure of something that isn't true, but I've done it. It's embarrassing and requires a great deal of humility to live it down. But indeed... If I believe I'm right I have a hard time letting go.

Thanks for the offer. They sound like good units that I would probably save in my stash and never end up using though No offence. You know how it is. I don't build much for myself and customers always get new parts. I usually use those aluminum chassis mount jobbies from Mouser. There are a couple of brands and I've used them both. Great for keeping the heat away from the filters.

I've managed what I'll call 20W with 470R screen grid R's on el84's. But that was with 400+Vp. An el84's life is measured in days when you run them like that. I had a box of fairly rugged old Sovteks and they would last between 50+ and -100 hours before they started to jingle and jangle from microphonics. Amazingly big sounding for such skinny bottles though.

I try to keep them right around 350Vp to 360Vp now. I use 470R screen grid R's even though 1K is said to be "safer". This seems to get good power (the "standard" 15W to 18W) and still hint at their unique character.

If you are indeed the sort that people eventually resent for your honesty, remember these two statements. They'll help you to maintain relationships.

1) "I'm not doing it to piss you off."

2) "Look into it for yourself."

[cyclone]

That's why I don't use them, no old parts but chassis and xformers, and I test the hell out of transformers I asked my lawyer what would happen if one of my amps burned someones house down. I was completely exposed to liability building "conversion" amps. The parts carry no liability if the eqpt is original. Repurposing it puts u in the hot seat, if you sell it to someone.

I have a heathkit decade box full of 10w wirewound resistors I use for experiments like that. Just thought I 'd offer, you said once you were on a tight budget and the cathode resistor assemblies are useful components to someone doing exactly what you do, in a lab environment. Not for customers.

I offer them up to any other knucklehead on here that wants them for their own research purposes, not to ebay them off or put them in equipment for sale. If i was an 18 watt guy (or gal, why not?) I'd build a box with a rotary switch.

I'm tactful enough, I appreciate the suggestions on how to accomodate fools, I'll never be good at itand I don't want to be! I just don't suffer fools well. Ignorance is fine, I'm ignorant about a lot of things.

[cyclone]

I'd like to explore distortion waveforms for 6bq5 output sections into an 8k load under various circumstances accompanied by sound clips to demonstrate the funky distortion sounds. Cheap euro soft vacuum pentode tubes "bend" more than beam tetrodes under similar voltage and current conditions. My opinion. My buzzy bugzapper distortion may sound like jesus's cello to someone else.

[Chuck H]

My buzzy bugzapper distortion may sound like jesus's cello to someone else.

That's where it gets SOOOO subjective. Example... I really like Mike Campbell's tone on the early Tom Petty albums. But if you listen to them really close you'll hear all manor of cross over distortion, some buzz that's been EQ'd down and more LF and HF ugliness than you think is there. In short, the mid and high mid character of the AC30 type sound is perfect for these tones, but comes with consequences! Attempts at idealizing the tone of an amp to fit that ideal in your head seldom work out. That is, trying to make an amp that gets it perfect at all frequencies under all overdrive conditions. I've come about as close as I ever expect to get

As to recordings... I do regret that I've never posted a sample of any of my amps here. I continue to intend to I have no recording media right now and I seem to get more and more out of practice. I play as much in two months as I use to play in a day!!! And that's no lie. I'm not sure my clips would shine like I want them to. And hearing past bad playing to decipher tone is an art unto itself!!! This I know.

[cyclone]

I know, i used to think I was Jimi on crack and one day I realized I was chicken feed. But, I do have an ear better than most, and I know shit when I hear it. Criticism sucks. If does but you might realize quickly that your criticism is just one wankers dumbass opinion and that your qualified opinion is the only one that matters, hang in there.

[Dave H]

Chuck H said -

"I'm an obsessive, truth-pounding asshole that people eventually learn to dislike"

I must be a slow learner then