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Post subject: Re: DRRI Redplating Problems
Posted: Thu Feb 09, 2017 2:15 am
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stratele52 wrote:
Don't put output tubes in the amp until you fix bias voltage issue.


+1

That's a great way to ruin an otherwise serviceable set of bottles.

Arjay

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Post subject: Re: DRRI Redplating Problems
Posted: Thu Feb 09, 2017 2:54 am
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Retroverbial wrote:
stratele52 wrote:
Don't put output tubes in the amp until you fix bias voltage issue.


+1

That's a great way to ruin an otherwise serviceable set of bottles.

Arjay


And Output Transformer wich receive 150 ma


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Post subject: Re: DRRI Redplating Problems
Posted: Thu Feb 09, 2017 2:56 am
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JZL, be sure you have the right fuse in the amp.


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Post subject: Re: DRRI Redplating Problems
Posted: Thu Feb 09, 2017 10:42 pm
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The bias voltage supply is reading -3.8mV. I take it that's pretty much a short right?


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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 2:09 am
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JZL wrote:
I take it that's pretty much a short right?


WTF?

:shock:

You should be measuring -49 VDC at TP5.

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: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 2:37 am
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JZL wrote:
The bias voltage supply is reading -3.8mV. I take it that's pretty much a short right?


The very first answer to your post show you everything you have to do about that .

Please read and follow.


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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 2:58 am
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stratele52 wrote:
The very first answer to your post show you everything you have to do about that .

Please read and follow.


We keep ringing the doorbell but I don't think anybody is home.

:?

Arjay

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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 3:30 am
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Retroverbial wrote:
stratele52 wrote:
The very first answer to your post show you everything you have to do about that .

Please read and follow.


We keep ringing the doorbell but I don't think anybody is home.

:?

Arjay


:lol:


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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 11:06 am
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stratele, I did follow your advice from the first post and turning the bias pot essentially does nothing. So now I am on your final piece of advice, "check bias circuit". I just didn't know how exactly to go about doing that. I'll figure it out.


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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 11:58 am
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To check if bias supply is good... pull all 6V6GT tubes first. Amp on secure bench, proper fuse in holder. Amp hooked to a speaker. Any 4-8 ohm speaker will due. You just need a load. Nothing plugged into any input. Volume(s) at zero. Bias pot set to half-way point.

First, measure the voltage at TP5 (see schematic). This is C- source near the power transformer. Should be -49VDC (+/- 5%). If not, you have a bad diode (CR1), bad drop-down resistor (R69), and/or bad bias filter cap (C36). Could even be a possible bad lead from power transformer. Or bad windings in PT. Though, I have never seen bad bias supply taps or winding in a PT before --- and the rest of the PT is okay. If voltages are okay move to...

Measure the VDC at TP36 (see schematic). This is the C- branch point, near the 6V6GT tubes. Should be -37VDC (+/- 5%). If not, could be a bad bias pot (R58) and/or dropping resistor (R59).

If all voltages read okay... check the voltage on pin 5 of each 6V6GT. Should be -30 to -40VDC. This is the usual voltage applied to Class AB1, push-pull 6V6GT operation.

If the voltages are bad but the resistor, cap, diode, pot all test okay... you may have the dreaded printed circuit problem. Turn amp off. DRAIN MAIN FILTER CAPS. Now, check for continuity issues. I've had this happen to me, on some amps. You may need to jump bad tracings. Or even build a small breadboard to bypass the bad portion of the main board.

http://ampwares.com/schematics/65_Deluxe_Reverb_RI.pdf


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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 12:23 pm
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BMW2002Ti thanks a lot for these instructions! I will do this today and report back.


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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 3:57 pm
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BMW2002Ti wrote:
First, measure the voltage at TP5 (see schematic). This is C- source near the power transformer. Should be -49VDC (+/- 5%). If not, you have a bad diode (CR1), bad drop-down resistor (R69), and/or bad bias filter cap (C36). Could even be a possible bad lead from power transformer. Or bad windings in PT. Though, I have never seen bad bias supply taps or winding in a PT before --- and the rest of the PT is okay.

I measured -4.5mV at TP 5. Any tips for checking the listed components? Do I need to lift either side of any of the components to get an accurate reading?


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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 4:50 pm
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The diode tests just fine. However I got R69 testing as 5.6 M-ohms, so that looks to be the culprit. It was not lifted out of the circuit but that shouldn't matter for this one.


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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 6:57 pm
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5.6 meg ohms indicates that the resistor popped. Better pull one leg and re-measure, just to be sure.

Main reason why components pop in the bias supply = short in 6V6GT caused excessive current draw in the bias supply. Components stressed and failed.

If this is what happened, you need to check all of the resistors and caps in this circuit. As well as the screen resistors and grid stoppers. R60, and 61 = grid stoppers. R62 & 63 = screen resistors.

Good luck!


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Post subject: Re: DRRI Redplating Problems
Posted: Fri Feb 10, 2017 10:44 pm
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BMW2002Ti wrote:
5.6 meg ohms indicates that the resistor popped. Better pull one leg and re-measure, just to be sure.

Main reason why components pop in the bias supply = short in 6V6GT caused excessive current draw in the bias supply. Components stressed and failed.

If this is what happened, you need to check all of the resistors and caps in this circuit. As well as the screen resistors and grid stoppers. R60, and 61 = grid stoppers. R62 & 63 = screen resistors.

Good luck!

The other resistors seem to test fine, I'm not quite sure how to go about checking the caps though. I will probably get around to putting a new resistor in on Monday and I'll let you know how it goes.


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