Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: fossilshark on June 21, 2024, 07:48:03 pm
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Hi all, got this peavey 5150III on the bench for a buddy, someone let the bass player go at it with a soldering iron and the negative voltage regulator was completely disconnected along with some very poorly installed plate resistor and diode clipping mods. After reconnecting the regulator (hoping it was that easy) the amp outputs nothing but an insanely loud hum no matter what knobs or switches are pressed.
I took out the 7915 (going to assume its bad) and took some voltage measurements.
All voltages on the 7815 are in spec as per schematic, but where the 7915 was im reading about +15vdc on pin 3 (measured against the ground pin), does this seem correct?
I just want to make sure all I have to order is a 7915 to get the heater supply working. Rest of the voltages on the tubes seems correct.
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First , it is not a Peavey , it is a EVH by Fender EVH5150-III
Complete schematic ; http://support.evhgear.com/schematics/EVH_5150III_AmpHead_Schematics.pdf
You must read -15 volts, not +15.
Your voltmeter's probe are they connected at the right place on the circuit ?
IMO, if 7915 was bad you did not read any voltage or not + or - 15.
You may have a broken connection between 7915 and the tubes heater
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yes, I double checked the meter polarity. The weird part is I am reading +15v where the -15v should be WITHOUT the 7915 installed. Will installing a new 7915 solve this issue?
Also thank you for the correction, I am not a fender or peavey guy.
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OK so I installed a new 7915 and the light now turns on, but relay K5 goes bonkers (switches very rapidly) when powered up. This is confusing.
Latole, the schematic you sent does not match this unit for some reason, it does not have K5 and also C16 is wrong, probably some other things but thats what tipped me off.
This is the correct schematic (from what I can tell) http://support.evhgear.com/schematics/EVH_50W.pdf
I am once again in over my head and requesting assistance. :icon_biggrin:
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Heres the rest of the K5 relay
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I am also going to start undoing these crappy mods. I would assume if one of these caused the problem then the previous owner would just undo them, however I am also confused by why they chopped off the negative voltage regulator for the heater circuit so :dontknow:
visible mods:
R82, R80, R72 replaced with 100K (these are plate resistors)
22uf cap across C16 (cathode cap)
R66 replaced with x2 1M resistors in series with antiparallel diodes across one of them (this resistor is connected to the grid of V3b)
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You do a good job.
Funny about the schematics , they have the same drawing number !
I'm too busy to come here often .
Look what drive the coil of K5
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Thank god they didn't give it to the drummer.