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Topic: A few tube questions... |
Mark Herrick
From:
Bakersfield, CA
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Posted 5 Jan 2004 11:15 am |
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Just acquired a Fender "Custom" Vibrasonic and, not wanting to leave well enough alone of course, I want to do some re-tubing. I remembered seeing the following post awhile back regarding a Vibrasonic:
http://steelguitarforum.com/Forum3/HTML/010308.html
My questions are as follows:
1. What does "ECG" mean in the designation of the "Phillips ECG NOS 6L6WGB JAN" tube? I have found Phillips 6L6WGB JAN tubes here:
http://thetubestore.com/
but they don't mention the "ECG". Is this the same tube?
2. Looking at the back of the amp and counting right to left, does it follow that the first tube is V1, second V2, etc? (I believe this is correct but I want to make sure.)
3. Based on #2 above, does this mean that the 5751 tubes mentioned in JD's post are in positions V1, V2 and V4 ?
4. I will probably take the amp to have it re-biased for the new power tubes, but I would like to learn how to do this myself. I have a digital volt meter; is this a better method than using a Bias Right or Bias King device? (Also, at the Fender Amp Field Guide, they mention the biasing on the "Custom" Vibrasonic as "Fixed, w/bias adjustment pot". What, exactly, does that mean?)
5. The power tubes in the amp now are Harma STR 6L6. I have never heard of these tubes. Does anyone have any info on or experience with them?
Any suggestions on where to look for biasing instructions/information and good places for purchasing tubes would be appreciated! |
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Ray Minich
From:
Bradford, Pa. Frozen Tundra
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Posted 5 Jan 2004 1:37 pm
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Phillips ECG is the complete name of the supplier. ECG has nothing to do with the part number.
For example, the name on my old ECG Semiconductor Master Replacement Guide is;
Phillips ECG, 1025 Westminster Drive, PO Box 3277, Williamsport, Pa. 17701.
However, I dont think they exist anymore. The replacement part business has been in a constant state of change since this 1991 manual was printed.
Regards... |
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Jon Light
From:
Saugerties, NY
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Posted 5 Jan 2004 1:50 pm
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You want 6L6GC, not WGB. The WGB is a lower powered tube with less headroom. Here is a preamp tube chart: http://www.kcanostubes.com/layout.htm
V6 is the one closest to the power tubes. |
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Jon Light
From:
Saugerties, NY
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Posted 5 Jan 2004 1:59 pm
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Let me revise that statement-----depends on what you're shooting for. I just read the thread you linked to and there is sense to what is said. We usually are trying to maximize our output and the GC is a natural choice in that direction. But if the earlier breakup and sweetness is an objective, well, it's there in that thread.
The Weber BiasRite is available without a meter--just jacks to plug your DMM probes into. I think it's a good choice (although I got the one with the built in meter). The #1 reason to go this way is that you don't need to drop your chassis and you don't need to muck around in the danger zone clipping onto hot tube pins with the power on. This stuff scares me. [This message was edited by Jon Light on 05 January 2004 at 02:07 PM.] |
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Mark Herrick
From:
Bakersfield, CA
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Posted 6 Jan 2004 9:25 am
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Thanks for the input.
I did find some info on the Harma STR 6L6 here:
http://www.watfordvalves.com/pdfs/tubetasting_el34_6l6gc.pdf
It might be a little dated, but the review seems to indicate a good tube; similar to GE 6L6GC and Phillips 6L6WGB.
Still wondering about that "Fixed bias w/adjustment pot" thing though...
Late breaking development:
Mike Kropotkin at KCA NOS Tubes says the Harma's are just re-branded JJ's...[This message was edited by Mark Herrick on 06 January 2004 at 09:48 AM.] |
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Roger Kelly
From:
Bristol,Tennessee
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Posted 6 Jan 2004 5:12 pm
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Mark....the "JAN" part of the tube number stands for "Joint Army Navy". Electron Tubes with this designation had to meet military Specifications, and thus are a more rugged built tube. FWIW  |
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Ken Fox
From:
Nashville GA USA
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Posted 6 Jan 2004 6:00 pm
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Fixed bias is the bias used in Fender Brown, Black and Silverface amps for the power tubes. Not all had adjustable bias (just the Blackface amps). The Browns were set via the bias resistor, no adjustment. Most Silverface amps had a bias balance pot. The other type is cathode biased, a self regulating bias, seen on all the preamp tubes and early Fender twees amps (power tubes).
V1 is the first tube to your right, facing the tubes from the rear of the amp.
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Mark Herrick
From:
Bakersfield, CA
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Posted 7 Jan 2004 8:30 am
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Thanks Ken.
Does this mean that if I use a Bias Rite device, I will get a certain reading for the bias on the power tubes that cannot be "changed", but only balanced across all the power tubes? Again, the amp is a Fender "Custom" Vibrasonic. |
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Ken Fox
From:
Nashville GA USA
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Posted 7 Jan 2004 8:53 am
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Your amp has a true bias adjustment, so the fixed bias can be set where you want it. Typically in the 30 to 35 ma range for a Twin/Vibrasonic. The schematic for your amp is on the Fender site, you can download it in PDF format:
http://www.mrgearhead.com/
I would also recommend 6L6GC tubes by JJ for this amp. They are possibly some of the finest new production tubes built today. In the past I used NOS tubes (RCA, Sylvania, etc. I became very disappointed with the inconsistencies; a lot of the preamp tubes would be microphonic. I am now more than happy with the quality and consistency of the JJ tubes. They are the only tube I use in my repairs. They will also withstand the higher plate voltages of a Twin/Vibrasonic (around 450 VDC) and even a 135 watt Twin/Vibrasonic (500 VDC on those amps).
[This message was edited by Ken Fox on 07 January 2004 at 09:00 AM.] |
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Mark Herrick
From:
Bakersfield, CA
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Posted 7 Jan 2004 9:18 am
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Thanks again, Ken.
In an effort to be able to try out some different tubes without having to take the amp to someone to be biased every time, I'm really interested in being able to do this biasing myself.
So, before I get in over my head, or further over my head, if I purchase one of these Bias Rite units, do I just hook that puppy up, install the tubes, power it all up and adjust the "bias adjustment pot" to get a 30mA - 35mA reading and I'm done?
(Or am I lying on the bottom of the pool waiting for someone to dive in and pull me out?) |
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Ken Fox
From:
Nashville GA USA
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Posted 7 Jan 2004 9:37 am
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That is how it is done. Just let the amp warm up good first. Check it a few days later, after the tubes burn in a bit. I use a Bias King, with two probes. I could not do without it!
I actually measure the plate voltage amd use a spread sheet to insert the tube types and values for each amp I work on. However, 30 to 35ma is about where ever Twin I have done lands at! [This message was edited by Ken Fox on 07 January 2004 at 09:39 AM.] |
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Mark Herrick
From:
Bakersfield, CA
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Posted 7 Jan 2004 10:00 am
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Very cool!
I was looking at this Bias Rite: http://www.webervst.com/bias.html
There is a model that allows switching between 4 tubes and also an option to switch between reading plate voltage and cathode current.
Would this do the job for me? It is slightly less expensive than the Bias King.
Thanks again for all the info! |
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Ken Fox
From:
Nashville GA USA
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Posted 7 Jan 2004 10:39 am
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| It looks great! I would have bought one, if they were available a few years back. The angle adapters would be nice for the old Bassman, Bandmaster, and Showman head cabs. They are not necessary for your amp. The VI option is great, as you can get plate voltage safely. That is handy when actually doing the "math" for current range. [This message was edited by Ken Fox on 07 January 2004 at 10:42 AM.] |
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Mark Herrick
From:
Bakersfield, CA
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Posted 7 Jan 2004 11:28 am
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Just placed the order!
Woo Hoo! |
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Jon Light
From:
Saugerties, NY
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Posted 7 Jan 2004 12:38 pm
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| Hey Mark--I got the 4-way that you dexcribed. I also got it with the feature that allows you to switch between the plate voltage readings and the cathode current (the VI option---$25). If you didn't go for it, I'd get back on the phone and do so. I'm so far over my head with this stuff--I think you and I are kind of in the same boat--we know and understand just enough to be dangers to ourselves and perhaps humanity---anyway, that switching option, if I understand what I'm doing, is the way to go. Actually, I'm confused because I don't understand how you would do the biasing without being able to switch between the two readings---Ken, can you help me to understand this? What good is a biasing meter like this without the ability to switch between pins to get your plate voltage and then your cathode current readings? (I sure hope I'm not looking too dumb). |
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Mark Herrick
From:
Bakersfield, CA
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Posted 7 Jan 2004 1:17 pm
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Hey Jon,
I did order the 4-way model with the VI option. I figured as long as I'm spending money, an extra $25 would probably be worth it in the long run.
I'm definitely over my head here, but maybe I can learn something before I permanently injure myself...
"Onward, through the fog..." --Oat Willie |
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