Super Reverb Voltages out of spec on VI and V2

Bandmaster, Bassman, Champ, Concert, Deluxe, Harvard, Princeton, Pro, Super, Tremolux, Twin, Vibrasonic, Vibrolux, Vibroverb and others

Super Reverb Voltages out of spec on VI and V2

Postby PeterMM on Tue Jan 17, 2017 2:54 pm

Hello Everyone,
Hoping to get advice/ direction. I've got an old Silverface Super Reverb, (blackface insides AB763) had it since 1970 or so. I'm in process of repairing it, Power supply electrolytics have been replaced. Also most of the usual recommendations, plate resistors/etc. have been done.

Problem is high voltage on preamp input on V1 & V2. I get 3.7 Volts on pins 3 & 8 of V1. Layout says it should be 2.1 V. I have replaced the 25-25 caps and 1500 resistors. I see 250 Volts on pin 6 (close to spec of 270) but 371 Volts on pin 1, which is way out of line.
What could be causing this?? (could it be something with input jacks and or volume pot)???

Going down the line, V3 is within spec with regards to pin 1 & 6 volatges.
V4 has 262v on pin 1 (should be 270v), but 195 v on pin 6 (again, should be 270v).
V5 has 376 v on pin 1 (should be 280v), and 376v on pin 6 (pretty close to the 390v).
Lastly, V6 has 268v on both pin 1 & 6, 102v on 3 & 8, layout says 106v.

I would greatly appreciate any advice!
Thanks for your time,
-Peter
PeterMM
Peasant
 
Posts: 1
Joined: Tue Jan 17, 2017 2:10 pm

Re: Super Reverb Voltages out of spec on VI and V2

Postby eolon on Sun Feb 12, 2017 3:16 am

but 371 Volts on pin 1, which is way out of line.
What could be causing this?? (could it be something with input jacks and or volume pot)???


If the plate voltage is too high, the first place I would look is the plate resistor. It should be 100K Ω. You will have to lift one end of the resistor to check its resistance; it may have drifted or failed.

Best Regards,

Don
eolon
Peasant
 
Posts: 28
Joined: Mon Sep 05, 2011 12:55 am
Location: Ohio

Re: Super Reverb Voltages out of spec on VI and V2

Postby tubeswell on Sun Feb 12, 2017 5:50 am

High voltage can be symptomatic of low tube current. What are all the plate, screen and cathode voltages, and HT supply node voltages for all the stages? And have you got proper AC filament voltages? And did you also replace the bias supply caps and diodes?
He who dies with the most tubes... wins.
tubeswell
Peasant
 
Posts: 41
Joined: Thu Dec 15, 2011 2:26 pm

Re: Super Reverb Voltages out of spec on VI and V2

Postby pdf64 on Sun Feb 12, 2017 4:52 pm

I suggest to verify (ie with a meter) that the plate and cathode resistors for V1 and 2 are the correct values.
It's very easy to misread colour codes, especially the modern 5 band E96 type.
Does the amp put any signal out?
My band:-http://www.youtube.com/user/RedwingBand
pdf64
Knight
 
Posts: 1243
Joined: Thu Dec 14, 2006 9:55 am
Location: Staffordshire UK

Re: Super Reverb Voltages out of spec on VI and V2

Postby stratele52 on Sun Feb 12, 2017 6:59 pm

Check V1 V2 cathode bias resistor. Value, good connection.
Very high resistor value or open circuit in the cathod resistor, give a high voltage reading at plate, or defective tubes.

PeterM , if you forget the voltage, did the amp work ?

You should read Power transformer voltage, sometimes it give more voltage to rectifier.
stratele52
Knight
 
Posts: 1904
Joined: Sat Aug 21, 2010 9:35 am
Location: Québec province, Canada


Return to Fender

Who is online

Users browsing this forum: No registered users and 3 guests