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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Thu Jul 24, 2014 5:03 pm
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Mowgli77 wrote:
My RCA 6V6GT tubes arrive any day and I don't know if they are 12 or 14 watt tubes as many references say different things. They are the grey plated 1950s tubes so I'm guessing they are 12?

I have 2 sets coming: one matched set are around 30mA and one set are around 50mA. Will the 30mA give me a lower ceiling/earlier break up?



The ones that test at 50mA will be stronger than the 30mA pair. PROVIDED the 6V6GT's were tested on the same tube tester. You'll know for sure, once you bias them on your amp. One pair will require more CW turn of the bias pot than the other pair.

As for the RCA 6V6GT, 12 watts max dissipation (for your push-pull Fender amp), is what I'd use. Adjust so your idle dissipation is around 8 watts per tube (around 70%). This is what sounds the best, to me. Using strong NOS tubes in Fender amps. Be sure to check for "red plating," overheating, and too early onset of overdrive.

Good luck! :mrgreen:


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Thu Jul 24, 2014 9:59 pm
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The '68 CDR schematic shows 407vdc. IN practice, My CDR measured 401 vdc with Tung Sol RIs, 397vdc with the stock GT/JJs. According to the Weber bias calculator, about 24.5 mA would be 70%. I set mine about 23mA to tame the noise floor a bit.
YMMV.


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Thu Jul 24, 2014 10:51 pm
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t-luxe wrote:
I set mine about 23mA to tame the noise floor a bit.


A wise decision, TL. I think you'll find that value will also extend the life of your tubes.

Arjay

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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Fri Jul 25, 2014 1:27 am
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t-luxe wrote:
The '68 CDR schematic shows 407vdc. IN practice, My CDR measured 401 vdc with Tung Sol RIs, 397vdc with the stock GT/JJs. According to the Weber bias calculator, about 24.5 mA would be 70%. I set mine about 23mA to tame the noise floor a bit.
YMMV.



Most of Fender amp sound good less than 60 % bias , Did you try and hear it ?


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Fri Jul 25, 2014 8:13 am
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stratele52 wrote:
t-luxe wrote:
The '68 CDR schematic shows 407vdc. IN practice, My CDR measured 401 vdc with Tung Sol RIs, 397vdc with the stock GT/JJs. According to the Weber bias calculator, about 24.5 mA would be 70%. I set mine about 23mA to tame the noise floor a bit.
YMMV.



Most of Fender amp sound good less than 60 % bias , Did you try and hear it ?


I did. In my case, 23mA was a compromise between tone and hiss. Certainly, some may prefer the bias a little colder. I went with the Tung Sols, but with the noisier GT/JJs, it sounded best(to me) around 22mA.


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Sat Jul 26, 2014 3:45 am
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t-luxe wrote:
stratele52 wrote:
t-luxe wrote:
The '68 CDR schematic shows 407vdc. IN practice, My CDR measured 401 vdc with Tung Sol RIs, 397vdc with the stock GT/JJs. According to the Weber bias calculator, about 24.5 mA would be 70%. I set mine about 23mA to tame the noise floor a bit.
YMMV.



Most of Fender amp sound good less than 60 % bias , Did you try and hear it ?


I did. In my case, 23mA was a compromise between tone and hiss. Certainly, some may prefer the bias a little colder. I went with the Tung Sols, but with the noisier GT/JJs, it sounded best(to me) around 22mA.



I never hear a hiss with matched JJ's with colder bias but each case ( amp , tubes ) are different that is why we must always check bias with new tubes


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Mon Aug 11, 2014 7:05 pm
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Compu Bias arrived today. Works great and I ordered the model that has 2 probes giving the read-out for each tube. I had acquired a few matched pairs of NOS 6V6GT tubes for use in my 68 Custom Deluxe Reverb Reissue recently so I was keen to see how well matched they were. All were very close but one pair that came from a well know tube dealer were way off. Here is what the reading was:

Tube 1: Vp:438, Current 20mA, W8.7
Tube 2: Vp: 439, Current 12mA, W 5.2

I was very disappointed that the 'matched' pair was not matched at all. The pair of tubes were all nicely labelled etc with all the matching stats written on the labels. This is the second time in a row this has happened with the same seller so not sure what is going on. To make sure it wasn't a variable I didn't see, I tried other known matched tubes and they all came out fine so I did get another mismatched pair...err. BUT the Compu-Bias sure is great.


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Mon Aug 11, 2014 7:21 pm
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Mowgli77 wrote:
...I was very disappointed that the 'matched' pair was not matched at all....BUT the Compu-Bias sure is great.


Ah! And that is exactly why we check....because it happens. :wink:

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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Mon Aug 11, 2014 10:33 pm
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Mowgli77 wrote:
This is the second time in a row this has happened with the same seller so not sure what is going on.


Were it me, I'd cross that vendor off of my list......permanently.

:evil:

Arjay

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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Mon Aug 11, 2014 11:41 pm
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Why is my vP 438? Seems high? Schematic says 407.


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Tue Aug 12, 2014 12:51 am
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Mowgli77 wrote:
Why is my vP 438? Seems high? Schematic says 407.


Is this the voltage, once the amp has stabilized over 10-15 minutes? Not sure about the '68 CDR, but my silverface DR reads 458VDC on the plates. It uses a 125P23B power tranny, a GZ34/5AR4 rectifier, & 4 stage 20/500 filter caps.

Image


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Tue Aug 12, 2014 1:04 am
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Mowgli77 wrote:

Tube 1: Vp:438, Current 20mA, W8.7
Tube 2: Vp: 439, Current 12mA, W 5.2

I was very disappointed that the 'matched' pair was not matched at all. ,.



Try to reverse them in case amp has defective resistor on one 6V6 circuit .

Let tubes in for few hours ," matched " bias may change by better or...worse


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Tue Aug 12, 2014 1:07 am
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BMW2002Ti wrote:
Is this the voltage, once the amp has stabilized over 10-15 minutes? Not sure about the '68 CDR, but my silverface DR reads 458VDC on the plates. It uses a 125P23B power tranny, a GZ34/5AR4 rectifier, & 4 stage 20/500 filter caps.


It would seem somewhat unusual to see an FEIC power tranny in a silverface Fender. My drip-edge '68 Deluxe Reverb's carries its original FMI P/N of 025130.

I have 435 VDC at the plates, using a vintage Mullard GZ34 and 16/475 Sprague's in the filter array.

Arjay

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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Tue Aug 12, 2014 6:00 am
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Yes I left he tubes in for at least 15 minutes and I tried swapping the positions. One tube is 8mA lower than the other.


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Post subject: Re: Max plate dissipation/bias? 68 Custom Deluxe Reverb Reis
Posted: Tue Aug 12, 2014 6:25 am
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Tube seller has offered me a full refund plus return shipping.
I still need a true NOS RCA 6V6GT black plate smoked glass pair. Can someone please suggest a reliable seller in US or Canada?


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