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Post subject: Blues JR III (2011) Red Plating V5 Only
Posted: Sun Feb 19, 2017 12:43 am
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I bought a Blues Jr for $150 bucks, found out the PCB traces on pins 3 and 8 clock wise (looking at down from the top at the rear of the amp) were burnt out of the trace (copper exposed)

I jumped wires from those pins to the ribbon cables. Amp now fires up without blowing fuses, emitting arcs or any noise. However, V5 keeps red plating. I retentioned the tube sockets, cleaned them out as well but still red plating.

R32 tested "dead" so i installed a new 220K ohm resistor. (after pulling that FREAKIN NASTY BOARD!!!)
But Im still red plating after 1 minute. Swapped tubes and red plating remains.

Can someone point me the right way? I can't even find a diagram online for the current models to know the the proper values of resistors. UGH!!!

Thanks Man, if all at possible.


Last edited by Ryan41018 on Sun Feb 19, 2017 2:50 pm, edited 1 time in total.

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Post subject: Re: Blues JR II (2011) Red Plating V5 Only
Posted: Sun Feb 19, 2017 4:05 am
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Be careful, lethal voltage in the amp


1- Remove both 6BQ5, Power amp ON .
You must read minus 10 Volts DC ( -10 Vdc) at pins 3 of 6BQ5 tubes . Or close, this is the bias voltage.
My schematic show it is TP24 where are two 220 K resistors, R 32 and R33. Be shure you got this reading on pins 3 too.

2- If you read -10VDC on both tubes, the red plating one is short, put a new 6BQ5.
Two news tubes are the best choice.

3-If you don't read -10 vdc, check bias circuit.

Do you have schematic and layout ? Did you know how to read it ?


Blues Junior Service manual ;

http://www.gitaarhobby.nl/gitaar-images ... Manuel.pdf


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Post subject: Re: Blues JR II (2011) Red Plating V5 Only
Posted: Sun Feb 19, 2017 8:57 am
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Readings at pin 3 on both sockets is zero. Installed new tube, still red plate. Read resistors r31 r32 while amp is on (volt settings) is -6.87vdc

On Ohm readings
R31 220k,
R32 -3.01

Not sure if why r32 is reading this way i just changed it last night.


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Post subject: Re: Blues JR II (2011) Red Plating V5 Only
Posted: Sun Feb 19, 2017 9:14 am
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Never never put power tubes if no bias voltage at pin 3 ( minus 10 volt DC ).
Fix bias voltage before. Unless you want to damage your power tubes

Don't you read my answer ?


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Post subject: Re: Blues JR II (2011) Red Plating V5 Only
Posted: Sun Feb 19, 2017 11:14 am
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Ryan41018 wrote:
Readings at pin 3 on both sockets is zero.


You have a *serious* bias-supply issue.

Investigate and repair before proceeding.

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: Blues JR II (2011) Red Plating V5 Only
Posted: Sun Feb 19, 2017 2:43 pm
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Can someone point me into the right direction to correct the bias supply? Like which resistors?


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Post subject: Re: Blues JR II (2011) Red Plating V5 Only
Posted: Sun Feb 19, 2017 2:49 pm
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stratele52 wrote:
Never never put power tubes if no bias voltage at pin 3 ( minus 10 volt DC ).
Fix bias voltage before. Unless you want to damage your power tubes

Don't you read my answer ?


How do i fix bias?

I know it involves changing resistors.....which ones?


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Post subject: Re: Blues JR III (2011) Red Plating V5 Only
Posted: Mon Feb 20, 2017 2:16 am
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With no minus 10 volts at pins 3 on both Output tubes, both tubes should redplate.
You write only one red plate ?

You did not answer to all questions;
Do you know how to read schematic and or layout ?

Like the like I write 19th feb
Blues junior service manual


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Post subject: Re: Blues JR III (2011) Red Plating V5 Only
Posted: Mon Feb 20, 2017 2:28 am
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The schematic version where I see R31, R32 is at the end of the service manual Drawing 0057275000

Bias circuit is here if I have the right schematic;
Image
Image


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Post subject: Re: Blues JR III (2011) Red Plating V5 Only
Posted: Mon Feb 20, 2017 2:31 am
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Read voltage a t TP33 minus 26.5 vdc or close. Report


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Post subject: Re: Blues JR III (2011) Red Plating V5 Only
Posted: Mon Feb 20, 2017 11:19 am
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stratele52 wrote:
Read voltage a t TP33 minus 26.5 vdc or close. Report



Strattele52 -

I read tp33 one side reads -27.7 and opposite side to the same resistor R51 (as shown in your shcemtatic) is -7.82


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Post subject: Re: Blues JR III (2011) Red Plating V5 Only
Posted: Mon Feb 20, 2017 11:29 am
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Ryan41018 wrote:
stratele52 wrote:
Read voltage a t TP33 minus 26.5 vdc or close. Report



Strattele52 -

I read tp33 one side reads -27.7 and opposite side to the same resistor R51 (as shown in your shcemtatic) is -7.82


Great, bias power supply work.

You should this -7.8 on both pins 3 of EL84.
Follow the circuit to find where you loos it


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Post subject: Re: Blues JR III (2011) Red Plating V5 Only
Posted: Mon Feb 20, 2017 12:05 pm
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stratele52 wrote:
Ryan41018 wrote:
stratele52 wrote:
Read voltage a t TP33 minus 26.5 vdc or close. Report



Strattele52 -

I read tp33 one side reads -27.7 and opposite side to the same resistor R51 (as shown in your shcemtatic) is -7.82


Great, bias power supply work.

You should this -7.8 on both pins 3 of EL84.
Follow the circuit to find where you loos it


Im Not reading -7.8 on pins 3 its -0.2 on both

When you say "find where you lose it" (-7.8) do you mean check TP 34, TP35, TP 36 etc? Same value -7.8?


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Post subject: Re: Blues JR III (2011) Red Plating V5 Only
Posted: Mon Feb 20, 2017 12:57 pm
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I do a mistake forget pin 3, we should work with pin 2 not 3 , bias -7 vdc are at pins 2 of each EL84; do you read it - 7 vdc ?

Sorry :oops:


- 7vdc go to C - at C33 on schematic.
C- go to R31, R32 just follow the way to pins 2;

R32 go to R34 by a connector and go to pin 2 of one EL84
R31 go to R33 by a connector and go to pin 2 of other EL84
At each resistor on these paths you must read -7 vdc


Both Cs- are show on this picture


Image


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Post subject: Re: Blues JR III (2011) Red Plating V5 Only
Posted: Mon Feb 20, 2017 1:36 pm
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I will try it and get back. Amp is home and Im at work.


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