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HH Scott 222c bias adjustment


JBryan
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Hey guys,

 

A while back, I sold a 222c to a fellow 'phile and he recently called asking about how he should go about biasing the amp. I've sent him the service manual and instructions and have tried to talk him through it but either I'm not explaining it well or he's a bit inexperienced and I think I'm just confusing him. Does anyone know of a video on youtube or such that I can send a link so he can actually 'see' the procedure? I've search but can't find anything specific to the 222c and find it difficult to believe that someone hasn't put a video up considering how many of these amps are out there. I'm too lazy and after looking through the handful of restoration videos on Youtube, I seriously doubt I could do justice to one. Any help would be most appreciated... Thanks!  

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Have him call me there is no actual bias adjustment built into a 222C unless it has been modified. All that is available adjustment wise is DC balance controls.Scott gave novice users no accurate way to adjust those controls. If I prequalify that the guy has some talent for this type of thing I'll guide him under the chassis on how to balance the pairs in a semi accurate way. No way will I send someone under the chassis with 450+ volts present if I don't feel comfortable with his abilities at such things. I don't need a claim on my liability policy and the sure rate hike!

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Thanks Guys. You're correct as usual Craig - Scott referred to it as a 'DC Balance Adjustment' but the procedure is similar to setting the bias. I did find a very brief segment in a 222c restoration video on Youtube and passed it along and then spent over an hour on the phone talking him through what shouldn't take more than 5 minutes. Quite the learning curve but I think he got it right in the end and he's still breathing so... its all good. Thanks again!

Edited by JBryan
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I propose measuring DCR from the output transformers centertap to each plate tap. Then while the amp is on with no signal measure voltage drop across said points.

I=V/R

Balance accordingly.

-Cindy

 

 

by the way this method is not the easiest or best method....but I am not giving you a free education...just like I wouldn't long ago with the reason why the center taps of the 6.3 Volt heater windings were only AC grounded in that Stereo VRD....you degraded the performance of amp you sold....

Edited by NOSValves
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NOSValves, stop harassing me. I don't care who you think I am or what you think I sold.

 

 

With you trying to get back at the person you think I am you in reality are actually only making yourself look worse. Especially technically.

 

Now if you want to have a real conversation about electronics then grow up and lets talk, or better post a schematic of what you are talking about. My understanding is you think in an indirectly heated tube the heaters need no DC reference? Heaters should not float; they should always have a DC reference (the simplest is just ground). Some people don't understand this and think that a capacitor to ground is sufficient. If they don't know what voltage their heaters are floating at, how can they know that they are within the heater-cathode voltage spec? Although they don't realise it, they are relying on leakage currents or insulation breakdown to set the heater potential. An example of this is in the Dynaco ST70 amp so if you have copied this bad habit form them then it's your problem.  If you know something that I don't please enlighten me.

 

Heater Circuit is on the last page.  http://www.thehistoryofrecording.com/Manuals/DynaCo/Dynakit_ST70.pdf

 

 

-Cindy

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Not a engineer and very happy to say I'm not.....if you happen to be one it will explain allot...I've met many of them and I think to date I liked and respected two of them. One is a Structural engineer and the other is indeed an electronics engineer. Now I am by no means saying all engineers are A-holes but if you are one......it sure will lower the standard of engineers in my book LMAO!!! 

 

See you CindyJarvis AKA xxxxJPMxxxx AKA The Slouth

 

PS: you knowing what I was referring too about then heaters absolutely proves you are indeed exactly who I say you are. 

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Post 7

 

 

 

the reason why the center taps of the 6.3 Volt heater windings were only AC grounded

 

 

Post 8

 

 

 

My understanding is you think in an indirectly heated tube the heaters need no DC reference? Heaters should not float; they should always have a DC reference (the simplest is just ground). Some people don't understand this and think that a capacitor to ground is sufficient. If they don't know what voltage their heaters are floating at, how can they know that they are within the heater-cathode voltage spec? Although they don't realise it, they are relying on leakage currents or insulation breakdown to set the heater potential. An example of this is in the Dynaco ST70 amp so if you have copied this bad habit form them then it's your problem. If you know something that I don't please enlighten me.

 

 

Post 12

 

 

 

you knowing what I was referring too about then heaters absolutely proves you are indeed exactly who I say you are.

 

 

 

You mean the heaters being only AC grounded that you mentioned in post 7?   

 

 

 

This is too easy, I thought you were a big shot tube amp guy the way you carry yourself, but honestly you aren't proving to me you know as much as you think you do. I also don't think this obsession with this other person "xxjpmxx"  is very healthy. What did this guy do to you? From my reading it looks like he ticked off a few other members but I can't seem to find anything where you two go at it. Can anyone shed some light on this for me and give me some links to the good stuff I seem to be missing.

 

-Cindy

Edited by CindyJarvis
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No that is not Mark he would know exactly why the center taps of the 6.3 volt are floating above DC ground... The Sloth..aka..xxxxJPMxxx...aka...CindyJarvis has no clue and actually thinks the measly 2 or 3 volts of DC makes a darn bit of difference in respect to damage or life to the tubes... its almost hilarious how this dude has book learning but no real expereince. I bet he is about a 20 year old snot nose kid at least he acts like it. Nothing wrong with that until you constantly disrespect people...... 

 

Heck we had a guy like this here 10 years ago named Ryan Inman...total electronics hack but knew all the basic lingo...he professed to have like 40 years experience! He was like 24 and living with his parents. He tried to sue anyone and anything that was involved in the tube business because of mercury poisoning from tube produce 70 or more years ago LOL!!

 

It wouldn't surprise me too much if this guy is one and the same. 

Edited by NOSValves
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CindyJarvis has no clue and actually thinks the measly 2 or 3 volts of DC makes a darn bit of difference in respect to damage or life to the tubes...

 

 

Once again please don't include me in your witch hunt. And personally myself and most competent engineers usually lift the center tap to around 50vdc and not 2-3v. And here I don't mind educating you because it appears you need it. Elevating the heaters will reduce hum by reducing or saturating the leakage current between heater and cathode. You know nothing about me so don't begin to think you do.

 

 

The laymen on here might be impressed with your bullying but anyone with a pinch of technical prowess can figure out you don't know bull. You act like a scared animal backed into a corner when presented with a technical question. But hey I get it, if you can't answer the question by all means attack the credibility of me but all it does is prove you know nothing and that you would be better off being a politician than an "amp tech".  

 

 

Everyday I am here you prove yourself more and more incompetent in my eyes. You can do two things, continue with this charade or just speak your mind and prove me wrong.

 

 

Oh and I do read your other posts and I find it a bit sad you have to drum up business the way you do, it's actually pitiful.

 

Someone needs more hugs in life or something  :P

 

 

-Cindy

Edited by CindyJarvis
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