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Post subject: plate voltage
Posted: Thu Mar 07, 2019 3:05 am
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Super reverb black face (anno 1966) Voltage plate (with tubes 6L6 in) is 435 instead of 465 as schematic says (With tubes out)
Any suggestion?
Thanks.


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 5:48 am
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Nothing wrong , plate voltage varies with tubes bias and with you house wall outlet voltage;

Colder bias = higher plate voltage
Hot bias = lower plate voltage

That is why we must alway read plate voltage when doing amp bias


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 8:13 am
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I know, but a drop of 20 volts seems too much to me.
Thank you.


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 8:35 am
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Francesco48 wrote:
I know, but a drop of 20 volts seems too much to me.
Thank you.


Power transformer could give lower voltage ; read AC volts , schematic show 360 volts AC
If you read 360 volts AC ;

1- Rectifier tube could be weak
2- Filter caps could be "weak" .
3- Your's 6L6s tube may drop too much (?) voltage


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 10:27 am
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Are you using a 5u4 or a gz34 for rectifier tube?
Is your negative bias voltage close to -52vdc?
Regardless, stratele is spot on.
Your within reasonable proximity to the schematics(+or- 20%).
Load up your other tube's and re-check voltages and confirm a stable bias.
Then tweak to your desired setting.
If you haven't replaced "all" the electrolytics, you probably should to prevent issues in the future.


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 11:25 am
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Always check fuse on old amps, last owner may put a too powerful fuse and amp is not protected.

This have nothing to do with the bias of course . :lol:


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 12:02 pm
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Is there some problem that caused you to check the plate voltage?
Is this a domestic or export amp?
Pictures would be a huge help. Inside the amp, and under the doghouse. (under the metal cover)

Regards,
vinyl


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 1:55 pm
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stratele52 wrote:
Francesco48 wrote:
I know, but a drop of 20 volts seems too much to me.
Thank you.


Power transformer could give lower voltage ; read AC volts , schematic show 360 volts AC
If you read 360 volts AC ;

1- Rectifier tube could be weak
2- Filter caps could be "weak" .
3- Your's 6L6s tube may drop too much (?) voltage
-GZ34 (a brand new one, works perfectly it gives 500 Volts when stand by is off) the 6L6s too are brand new.Filter caps are Ok


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 1:58 pm
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And the filter caps?

Arjay

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"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


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 2:05 pm
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Rectifier tube is GZ 34 and it's brand new, 6L6s too are brand new.
Caps are some year old but they look good.
Rectifier, when stand by switch is off, gives 500 DC volts.
But when I switch it on voltage goes down to about 435 instead of 465.
another curios thing is that when i switch stand by off voltage goes to 0 immediately!
I mean caps discarge in a few seconds.
Thanks for helping me.


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 2:19 pm
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Francesco48 wrote:

another curios thing is that when i switch stand by off voltage goes to 0 immediately!
I mean caps discarge in a few seconds.
Thanks for helping me.


Too much load on circuit voltage IMO
Some "light" short circuit somewhere. Amp must see a tech/ somebody who know how to fix amp

Be sure amp have the right fuse.
Any mods on the amp ?

Post some good pictures


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 4:52 pm
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vinyl wrote:
Pictures would be a huge help. Inside the amp, and under the doghouse. (under the metal cover)

stratele52 wrote:
Any mods on the amp ?

Post some good pictures

Retroverbial wrote:
And the filter caps?

Arjay

Francesco48 wrote:
Caps are some year old but they look good.
Rectifier, when stand by switch is off, gives 500 DC volts.
But when I switch it on voltage goes down to about 435 instead of 465.
another curios thing is that when i switch stand by off voltage goes to 0 immediately!
I mean caps discarge in a few seconds.
Thanks for helping me.


Perché quello che hai postato, credo che tu abbia bisogno di nuovi tappi elettrolitici. Non parlo italiano, ma credo anche che l'italiano sia la tua prima lingua.


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Post subject: Re: plate voltage
Posted: Thu Mar 07, 2019 7:24 pm
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Look for damage at your V9 tube socket (the rectifier). The problem may lie there. Check all soldered tangs and the dielectric insulator itself for cracks or chips.

Arjay

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"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


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Post subject: Re: plate voltage
Posted: Fri Mar 08, 2019 2:37 am
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vinyl wrote:
vinyl wrote:

Perché quello che hai postato, credo che tu abbia bisogno di nuovi tappi elettrolitici. Non parlo italiano, ma credo anche che l'italiano sia la tua prima lingua. ...Anno 1966 )


Translation ;

Because what you posted, I think you need new electrolytic filter caps. I do not speak Italian, but I also believe that Italian is your first language....( Anno 1966)


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Post subject: Re: plate voltage
Posted: Fri Mar 08, 2019 3:05 am
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stratele52 wrote:
vinyl wrote:
vinyl wrote:

Perché quello che hai postato, credo che tu abbia bisogno di nuovi tappi elettrolitici. Non parlo italiano, ma credo anche che l'italiano sia la tua prima lingua. ...Anno 1966 )


Translation ;

Because what you posted, I think you need new electrolytic filter caps. I do not speak Italian, but I also believe that Italian is your first language....( Anno 1966)
Grazie!!!


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