blackface twin reverb,still bad sounding

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blackface twin reverb,still bad sounding

Postby strangedays on Thu Mar 16, 2017 6:17 pm

At last,new power tubes arrived. I've just installed them,rebiased the amp(there are few good methods on the net) .New speakers installed(Weber C12N clones),Completely recapped (F&T & Sprague right values).All the preamp tubes are new,pots cleaned but the amp sounds as bad as before.Mushed,muffled,midgy and with no top end.At This point i suspect there is one or more damages and it's time to contact a good technician.If you have any more suggestion before i find someone competent on vintage amps,i'll apprecciate very much.
Are there any other componets to replace by myself ? In my opinion i've done all i could.From what i've heard it's impossible a blackface sounds this way.
Thank you.
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Re: blackface twin reverb,still bad sounding

Postby Dean Jr. on Fri Mar 17, 2017 4:49 pm

Have you made a voltage chart? Does the am p sound the same way in both channels?
Worst case scenario is that you have a bad output transformer. Yes, an OT can be bad and still produce sound...just not what we would want to hear.
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Re: blackface twin reverb,still bad sounding

Postby stratele52 on Fri Mar 17, 2017 5:31 pm

Bad Output transformer as Dean jr wrote.
Bad voltages
Bad resitors in phase inverter circuit
To name few

On both channel ?
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Re: blackface twin reverb,still bad sounding

Postby strangedays on Fri Mar 17, 2017 7:58 pm

Yes that's right The amp sounds bad on both channels.Ater the recap work i consider it could be the tranformer too.
In that case what could i do?
New transformer?
Try to repair?
Thanks a lot for reply.
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Re: blackface twin reverb,still bad sounding

Postby stratele52 on Fri Mar 17, 2017 8:23 pm

Find which are the bad parts before. You work like a blindman and you spend more money than if you see a qualified tech with no result.

I did not write it is the Output Transformer. I may be a lots of thing and we have not enough information.

First, which Blackface circuit ?
Second , read all B+ voltage and report. Be careful, lethal voltage in tubes amp.
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Re: blackface twin reverb,still bad sounding

Postby strangedays on Fri Mar 17, 2017 9:19 pm

Stratele 52 i was only asking information about the transformer in general,i din't mean to replace it or repair by myself.Anyway you're right, i'll go to a technician. at this point is the fairest thing to do.
At athe moment i don't have the chance to measure the voltage but my blackface is an ab763.
Thanks a lot for replies.
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Re: blackface twin reverb,still bad sounding

Postby tubeswell on Tue Mar 21, 2017 5:34 pm

Don't start throwing away transformers yet. theres still a few other things you can look at.

What B+ voltage and bias supply voltage have you got?

Have you changed all the electrolytic caps (including in the bias supply?)

Re-tensioned all the tube socket pin clamps?

Checked the old coupling caps for DC-leakage (I found an old 0.022uF in a 67 super reverb was leaking 1.6VDC recently, made heaps of difference to the volume in that channel)
He who dies with the most tubes... wins.
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Re: blackface twin reverb,still bad sounding

Postby Dean Jr. on Tue Mar 21, 2017 6:58 pm

+1 with tubeswell. When I Mentioned the OT, that was a 'worst case scenario'....meaning it would not be the fist thing I would start taking out while wondering.
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Re: blackface twin reverb,still bad sounding

Postby drewleslie on Wed Mar 22, 2017 12:34 pm

I keep good OTs around ... it only takes 5 min to patch it in and be sure. Especially with so many bases already covered. Dirty speaker jack? drew
How can you tell the difference between a chemist and a plumber? Ask them to pronounce 'unionized'.
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