Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fkitch on December 29, 2023, 11:16:35 am
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Merry Christmas everybody,
Ok, after successfully (thanks to you of course!) completing my first tube amp repair I am now onto a new project.
It's a Spain made, early 60s most probably, 8 tube 'Contrafon 750' head . No info available at all online but I was told by the owner it may be a AC30 clone?
Has 4xEL84 power amp, 2xECC83 preamp, 2xEZ81 rectifiers
Would be possible to ascertain from the pictures if a particular model could have 'inspired' this one please? I have no experience on VOX amps at all, but can't seem to find AC30s dual rectified.
Briefly powered it up, there's strong hum and sporadic frying pan noise. Very dark sound, I used an 8ohm speaker.
thanks!
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Hi
I have the same amp. Mine is in worst shape even...
Is a pending project, but i found this schematic time ago.
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If I were to guess, I'd say it looks like a PA. Some might think that PA stands for Public Address while others might say it stands for Power Amp (Like for an organ preamp or something like that). Whatever, it looks like it could be either.
It has two rectifiers because the manufacturer decided for whatever reason, that it wanted to use 6.3 volt filament rectifiers and EZ81 was common and cheap. But providing enough power to run 4XEL84 was a bit much for just one.
Edit - At another glance, the amp you have and the schematic provided by Chocopower are not the same amp. On the schematic I see one 12AU7 and on your amp, I see two 12AX7
Dave
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> strong hum and sporadic frying pan noise.
Main filter caps, then clean the sockets and change tubes.
Since it surely worked in 1959, and parts values are readable, you don't urgently need a schematic just to get it playable again. Just fix what's broken, rotted, or tarnished.
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Amplificador Valvulas Años 50(Contrafón)
https://es.wallapop.com/item/amplificador-valvulas-anos-50-contrafon-478114903
He likes it a lot, but he should, since he is asking 500 Euros. Not the same product, but same brand and probably same factory.
Somewhere I saw a date of 1966, which with those rectifiers and history of Spain makes more sense than the "1959" I spouted above.
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Its a bass amp, or as the name says, contrabass.
Mine came with a matching 2x15 cab and 2 12au7.
The "schematic" i post is one i found in the web.
Is just the preamp
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* i din't vandalized the cab..
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JOBESONIK is the brand
Joaquin benavent sonic
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* i din't vandalized the cab..
Wow! Yes looks like a bass cabinet
Would you happen to have a picture of the interior of the amplifier? To compare components with mine…
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I think it’s a version of this, with just one channel with one input and two tone controls instead of one
(https://static.wixstatic.com/media/ad89e3_e400b043272c40fda2791621a87d5493~mv2_d_3508_2480_s_4_2.jpg/v1/crop/x_1,y_0,w_3505,h_2480/fill/w_3505,h_2478,al_c,q_90,enc_auto/ad89e3_e400b043272c40fda2791621a87d5493~mv2_d_3508_2480_s_4_2.jpg)
I will start with filter caps and tubes and let’s see, need to investigate tone stack potential mods to make it more guitar friendly.
Thank you all for your help and inputs, much appreciated!
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I'll do. Just need some days..
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You could try reducing the .15 coupling caps to the output tubes. .1, .068, .047, .022. ...?