It is currently Mon Mar 16, 2020 10:51 am

All times are UTC - 7 hours



Post new topic Reply to topic  [ 41 posts ]  Go to page 1, 2, 3  Next
Go to page 1, 2, 3  Next
Author Message
Post subject: Pro Reverb (pulling my hair out!)
Posted: Mon Aug 08, 2016 4:31 pm
Offline
Amateur
Amateur

Joined: Sat May 25, 2013 10:02 pm
Posts: 197
Loud hum when I turn on standby, I've checked the tubes, the caps (under the dog house)have recently been changed. rectifier been changed. Pull one power tube at a time and still hums.

Pulled pre amp tubes one at a time, even with that one tube out noise still appears when taken off standby.

I checked the bias with my Dr Tube Bias Master....148!!!! I shut it down.

Any input would be appreciated.
:?: :?:


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Mon Aug 08, 2016 6:26 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26416
Location: Tombstone Territory
Ryan41018 wrote:
I checked the bias with my Dr Tube Bias Master....148!!!! I shut it down.


Do you recollect what plate voltage your power tubes were pulling?

It does sound like a P/S issue or perhaps a problem with the bias circuit.

What kind of shape is your rectifier in?

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Mon Aug 08, 2016 6:38 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Ryan41018 wrote:
Loud hum when I turn on standby, I've checked the tubes, the caps (under the dog house)have recently been changed. rectifier been changed. Pull one power tube at a time and still hums.
Pulled pre amp tubes one at a time, even with that one tube out noise still appears when taken off standby.Any input would be appreciated.
:?: :?:


I think you have one output tube which is shorted. Do you have access to a tube tester? Or a set of known, good pair of 6L6GC tubes to try? They don't even need to be precisely matched. Just to try out in the amp. If same buzzing with another pair --- turn off and don't use amp. Prolly power supply, output stage, or bias supply issue(s). Need tech to look at it.

Don't use the amp until you can get the tubes tested. Or have another set to try. Or can get the amp to a tech.

Good luck!


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Mon Aug 08, 2016 8:25 pm
Offline
Amateur
Amateur

Joined: Sat May 25, 2013 10:02 pm
Posts: 197
New tubes have been tested. Hum begins after warm up and only after turning on the standby switch. I don't know what the voltages are on the tubes. Heck, I don't know how to check them with my Fluke meter.

All the chassis grounds are connected, so its not those. if I turn both the standby and power on at the same time (while its warming) the hum will increase as the tubes get hotter. Again I tested with my Bias probe looking for 25MA, but now way it was 140. Seems to be bias related.


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Mon Aug 08, 2016 8:34 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
New tubes or not --- sounds like a short. You have another pair of good (non-shorted) 6L6GC tubes? Try them. My bet is the amp doesn't hum and start going crazy with the bias readings.

If the hum and increasing bias setting number still happens with the other set of tubes --- look at the sockets. You may need to tighten or replace them. Poor contact = no bias control.

If sockets are ok... look at the bias power supply. Bad pot. Bad caps in the supply.

Problem is prolly in those areas, above. If not... you have issues with PSU and or output stage. Rule out tubes, then sockets, then bias supply first.


Good luck! Keep us posted. :mrgreen:


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Mon Aug 08, 2016 8:38 pm
Offline
Amateur
Amateur

Joined: Sat May 25, 2013 10:02 pm
Posts: 197
I did put BRAND NEW tubes in it. Cant be the tubes.

I will check the tube sockets first. I don't know what resistors/caps are Bias supply.

Heres exactly what it sounds like

https://youtu.be/WwlfeaYQimQ


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Mon Aug 08, 2016 8:56 pm
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Brand new tubes have been known to have shorts. Try a known, good pair.

Hum is bad. Prolly worse in person. But, the 100+mV bias reading is indicative of a tube short. Or no bias supply voltage on the tube grids. Either due to poor contact with sockets or defective bias power supply.

Do you have any electrical contact cleaner that you can try on the socket tangs?

Report back. Good luck! :)


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Mon Aug 08, 2016 10:04 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26416
Location: Tombstone Territory
BMW2002Ti wrote:
But, the 100+mV bias reading is indicative of a tube short.


Or a bias-supply cap installed backwards (ie: incorrect polarity). This cap *must* be wired with the positive "+" side connected to ground.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Tue Aug 09, 2016 8:00 am
Offline
Amateur
Amateur

Joined: Sat May 25, 2013 10:02 pm
Posts: 197
Thanks for the dialogue guys, i jumped in a 100uf 100V cap onto the 50uf that sets just next to the pilot light in the chassis and viola noise gone. So I just replaced it and I've set the bias to 25ma and she purrs like a kat!


:mrgreen:


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Tue Aug 09, 2016 9:32 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
That is prolly the bias supply filter cap. Position is something like this?

Image


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Tue Aug 09, 2016 9:50 am
Offline
Amateur
Amateur

Joined: Sat May 25, 2013 10:02 pm
Posts: 197
Yessir that's it.


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Tue Aug 09, 2016 10:37 am
Offline
Amateur
Amateur

Joined: Sat May 25, 2013 10:02 pm
Posts: 197
Thank you guys for all your input and pointing me into the right direction.


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Tue Aug 09, 2016 10:39 am
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26416
Location: Tombstone Territory
Glad you've got the amp working again.

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Tue Aug 09, 2016 10:55 am
Offline
Amateur
Amateur

Joined: Sat May 25, 2013 10:02 pm
Posts: 197
New problem - amp wants a 2 amp fuse, the previous owner had a 3 amp. I turned on the power switch (not standby) and blew a fuse.


Top
Profile
Post subject: Re: Pro Reverb (pulling my hair out!)
Posted: Tue Aug 09, 2016 10:56 am
Offline
Rock Star
Rock Star
User avatar

Joined: Sat Jul 03, 2010 2:18 pm
Posts: 6544
Did you take the old cap out of the amp?


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 41 posts ]  Go to page 1, 2, 3  Next
Go to page 1, 2, 3  Next

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: