Blackface twin reverb dark sound

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Blackface twin reverb dark sound

Postby strangedays on Fri Oct 07, 2016 1:28 pm

Hi,i've just purchased a 1967 blackface twin reverb.I notice it' sounds right when i turn it up,sparkly and clear. but after a while (20/30 minutes) it starts to deliver a muddy sound with loss of Harmonics and lot of mids.The amp has been completely recapped from what i've seen.The preamp tubes are all new but i don't know in which condition are the output tubes.Could the output tubes be the cause of the muddy sound in the case ? As i've said before the amp sounds right as i turn it up,but the more i play the more it gets darker.
Thans alot everyone.
Cheers.
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Re: Blackface twin reverb dark sound

Postby pdf64 on Fri Oct 07, 2016 6:58 pm

Maybe the power tubes are idling too hot, or the bias supply cap is still original and gets leaky as it warms up, running the power tubes ever hotter - do you have a bias probe available to check that (safely, ie without operating the amp outside of its cab)?
As with any newly acquired item of vintage electrical equipment, best to get it checked over by a competent tech.
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Re: Blackface twin reverb dark sound

Postby strangedays on Fri Oct 07, 2016 8:31 pm

pdf64 wrote:Maybe the power tubes are idling too hot, or the bias supply cap is still original and gets leaky as it warms up, running the power tubes ever hotter - do you have a bias probe available to check that (safely, ie without operating the amp outside of its cab)?
As with any newly acquired item of vintage electrical equipment, best to get it checked over by a competent tech.


Tanks for reply,the amp has benn completely recapped,bias cap included.i don't know if the caps values are proper anyway. Only the coupling caps are original.I'm agree with you that a technician should bias it.
Cheers.
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Re: Blackface twin reverb dark sound

Postby pdf64 on Fri Oct 07, 2016 10:57 pm

If you're playing loud, it may just be that the speakers are getting rather hot; that can change their resistance and can change their tone by affecting how the amp interacts with them.
When the dark tone becomes apparent, check how hot the speaker magnets are (take care they may be too hot to touch for more than a moment!).
Vintage type speakers tend to be more affected by this effect than more modern speakers, with high power, ventilated voice coils.
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Re: Blackface twin reverb dark sound

Postby stratele52 on Sat Oct 08, 2016 9:40 am

pdf64 wrote:
As with any newly acquired item of vintage electrical equipment, best to get it checked over by a competent tech.



+1000
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Re: Blackface twin reverb dark sound

Postby stratele52 on Sat Oct 08, 2016 9:43 am

strangedays wrote:
Tanks for reply,the amp has benn completely recapped,bias cap included.i don't know if the caps values are proper anyway. Only the coupling caps are original.I'm agree with you that a technician should bias it.
Cheers.



Bias and complete check up by a qualified tech. There are too many unqualified guys work on a amps.

Recaping caps without knowing wich brand and value ( where are the pictures ? ) do not help. To many guy put cheap brand.

Pictures please.
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Re: Blackface twin reverb dark sound

Postby strangedays on Sat Oct 08, 2016 12:03 pm

stratele52 wrote:
strangedays wrote:
Tanks for reply,the amp has benn completely recapped,bias cap included.i don't know if the caps values are proper anyway. Only the coupling caps are original.I'm agree with you that a technician should bias it.
Cheers.


Thanks,i'll post some pics as soon as possible.
Cheers.

Bias and complete check up by a qualified tech. There are too many unqualified guys work on a amps.

Recaping caps without knowing wich brand and value ( where are the pictures ? ) do not help. To many guy put cheap brand.

Pictures please.
strangedays
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Posts: 83
Joined: Mon Sep 01, 2008 10:04 am

Re: Blackface twin reverb dark sound

Postby stratele52 on Sat Oct 08, 2016 12:19 pm

A good reputation tech; Skip Simmons write ;


http://www.skipsimmonsamps.com/truthabo ... eamps.html
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