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Post subject: Re: Bias setting
Posted: Sun Dec 23, 2012 10:54 pm
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BMW2002Ti wrote:
1964 Tremolux! That amp is crying for some "Texas Flood." :D


http://www.youtube.com/watch?v=tWLw7nozO_U


+1!

And everybody building clones of SRV's "number one" take note -- it looks like his bottom tone control knob was a new white or parchment replacement. I never caught that before.

Arjay

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Post subject: Re: Bias setting
Posted: Fri Dec 28, 2012 6:53 pm
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What is the proper way to play through both the tremolux and dual showman at the same time?

Thanks


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Post subject: Re: Bias setting
Posted: Fri Dec 28, 2012 7:16 pm
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Jumper INPUT 2 from one amp to INPUT 1 of the other?


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Post subject: Re: Bias setting
Posted: Fri Dec 28, 2012 7:32 pm
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Matt, I'd suggest an A-B-Y box that is capable of isolating the ground between the amps. And using the shortest cable length as possible. A box with phase shifting capabilities may also be helpful....Beemer posted while I pecked away at the keyboard! I read the word"proper", and went overboard!!! Art

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Post subject: Re: Bias setting
Posted: Sat Dec 29, 2012 12:18 am
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aclempoppi wrote:
Matt, I'd suggest an A-B-Y box that is capable of isolating the ground between the amps. And using the shortest cable length as possible. A box with phase shifting capabilities may also be helpful


+1

The Radial Big Shot is a quality A/B/Y stompbox that's rugged, reliable, and reasonably priced. I've been using one for about five or six years now and it was the best $75 I ever spent on an accessory. It will instantly transform any vintage two-channel Fender amp into a footswitch-controlled channel-selectable tone machine or conversely permit the operation of two independent amps in tandem.

Arjay

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Post subject: Re: Bias setting
Posted: Sun Dec 30, 2012 6:00 pm
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The reviews for the Radial Engineering BigShot are very good. In looking for a DIY TS808 I came across BYOC Amp Selector & Stereo FX Router, http://www.buildyourownclone.com/ampselector.html

TS808
http://www.buildyourownclone.com/overdrive.html

What do you guys think? Again, thanks!


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Post subject: Re: Bias setting
Posted: Mon Dec 31, 2012 3:38 pm
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Retroverbial wrote:
For your Tremolux, you should measure -45 VDC at the wiper of the bias pot -- the Showman's should be -52 VDC. The actual current draw of the output tubes will be contingent upon a number of factors, not the least of which is the brand and type of glass used. Another factor which will determine the amp's idle bias is the age of the components and how much they've drifted in value over the years. For NOS RCA blackplates or Fender-branded Sylvanias, 37.5 or 38 mA might be optimum. Newer glass like Winged C's, Sov-Tek, or EHX might be more comfortable at 33 or 34 mA.

HTH

Arjay


Having trouble with the DS. Plate voltage is -45.5V not - 53V and bias range is 0- 20mv. The amp is noisy at idle somewhat a 60cycle hum and a buzz. Any help is greatly appreciated. House wiring is good, verified with tester and the Tremolux.

Thanks

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Post subject: Re: Bias setting
Posted: Mon Dec 31, 2012 3:42 pm
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Yeah Matt, that amp selector looks good to me. I'm not a pedal guy, so I'm not sure about the Tube Screamer clone. But hey, it's probably worth the build! Art

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Post subject: Re: Bias setting
Posted: Mon Dec 31, 2012 4:32 pm
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MattGuitarKy wrote:
[Having trouble with the DS. Plate voltage is -45.5V not - 53V and bias range is 0- 20mv. The amp is noisy at idle somewhat a 60cycle hum and a buzz. Any help is greatly appreciated. House wiring is good, verified with tester and the Tremolux.


Suspect the bias supply. Check the electrolytic cap, the diode stack, the pot, and all associated wiring. Excessive idle noise can be a byproduct of bias-supply problems. I'm not certain about the hum/buzz issue......there may be other (unassociated) factors at play.

HTH

Arjay

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Post subject: Re: Bias setting
Posted: Mon Dec 31, 2012 9:17 pm
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Matt, one other thing. The sockets. How old are they? Try a little contact spray.

They may need tightening --- you have to discharge caps, first.

Good luck and Happy New Year!


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Post subject: Re: Bias setting
Posted: Mon Dec 31, 2012 10:16 pm
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Original as far as I know. The pins do move slightly when checking for loss wires.

Happy New Year to all.

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Post subject: Re: Bias setting
Posted: Tue Jan 01, 2013 5:02 am
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Try a little CAIG GN-5. Then, check the bias for consistent value. If still issues... may need to tighthen or replace those sockets. Be sure the cap in the bias supply is fresh. 100mfd/100VDC F&T's are nice for these amps.

And use a little good contact cleanre for pots (I like CAIG Fader Lube) in the bias pot. Don't use plain contact cleaner on any pot. these dry out the OEM lube and can eat and pit the carbon contacts inside the pot mechanism.

Good luck with that great amp. If you need sockets, I have a bunch of 1-1/8 inch diameter hole mil spec micanol Amphenol puppies. Use the best for this amp. No Chinese stuff, PLEASE!!!!!


http://www.amazon.com/DeoxIT%C2%AE-GOLD ... DEoxit+GN5

http://www.amazon.com/DeoxIT%C2%AE-Fade ... B000H2G5R8


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Post subject: Re: Bias setting
Posted: Tue Jan 01, 2013 7:25 pm
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Concur with the previous suggestions. Guess I'd check the 470-1watt resistor, the 10k pot, the 27K resistor on the bias adjust pot, the two 220K 5% grid resistors, and the two .1 coupling caps. Of course, the electrolytic, diode, and solder joints are part of this test. After the bias supply is cleaned up, if the power section tubes are all good, the 60 or 120HZ hum can be addressed. Happy Hunting!!! Art

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Post subject: Re: Bias setting
Posted: Sun Jan 06, 2013 6:07 pm
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Ok, new info. The bias pot measures 10k-1. Resistors, diode and cap in bias circuit all check. Diode pass value .5 volts is this ok? Cleaned all pots with Deoxit.

What I didn't check was channel 2. It is at 1/2 power compared to channel 1 at the same volume knob level. Swapped out preamp tubes with other good tubes no change. What do you guys think?

Again, thanks!

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Post subject: Re: Bias setting
Posted: Sun Jan 06, 2013 7:08 pm
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Matt, dang... I had this beautifully eloquent explanation. And it went POOF! Into the ether of InterNet.

Anyhow, are we talking about input 1 and 2 of one channel (NORMAL or VIBRATO). Or the inputs of NORMAL versus VIBRATO?

We're move on from there with some ideas. :D


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