100 watt Plexi-clone &

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aerojazz
Senior tube assistant
Posts: 150
(3/2/04 2:00 pm)
 100 watt Plexi-clone
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 Hi gang, A number of times I have read posts that gave me the impression that one could power up a new build without tubes. I'm probly the least knowlegable member here, so please bear with me. I do have a variac and I am going to wire in my own bias voltage. My questions are:
1. Does powering up without tubes harm the trannys?
2. Will I be able to verify bias voltage without tubes durring this process.

Thanks
 
coap01
Junior tube assistant
Posts: 106
(3/2/04 2:47 pm)
 power up
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 you should read the powerup procedure that paul ruby has on his site. www.rubyamplification.com/info.html he answers all your questions in his text

--Lev
 
HotBluePlates
I only work on Fender's
Posts: 698
(3/2/04 5:14 pm)
 Powerup without tubes
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 As quick help for those on the board, here's some points to remember:

1. Powering up without tubes will not harm your amp. This will give you a chance to check for proper voltages at all tube pins, and may help you spot shorts (especially if you blow fuses). It also keeps tubes from being damaged in the case of wiring errors.

2. All B+ voltages will be higher than expected, because there are no tubes in the amp to draw current and load down the power supply. This is to be remembered when you check preamp tube voltages, and find the plates to have the full B+ or close to it. These will drop once tubes are plugged in.

3. For fixed biased amps, you can check for bias voltage on the grid pin of the tube socket (pin 5 in 6V6 and 6L6). a good starting voltage to have is 1/10th of the plate voltage. So with 450v of B+, look for around -45v on pin 5. The voltage could be higher or lower, but be wary of half or double the expected bias voltage. This will give you a chance to double check the bias circuit.

One last point: The bias circuit draws very little current, so the bias voltage with tubes out should be very close to bias voltage with tubes in.
 
aerojazz
Senior tube assistant
Posts: 154
(3/4/04 5:18 pm)
 Re: Powerup without tubes
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 Yea, thanks for that
 
aerojazz
Senior tube assistant
Posts: 155
(3/4/04 7:58 pm)
 Re: Powerup without tubes
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  The two 56K resistors on the second set of 50/50 caps, what kind of range do I have there?
I don't have any 3 watt 56k's

Edited by: aerojazz at: 3/5/04 7:19 am
 
 
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