Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: SLW on November 24, 2013, 03:55:23 pm
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I just finished building a 5E9A. I put the 5Y3 in it and powered it up using a lamp limiter. It looked good. I measured 420VDC. I put the rest of the tubes in and powered it up again. This time the lamp glowed. I measured 300VDC. I started pulling tubes and measuring. With the two 6V6's pulled and all of the preamp tubes installed the lamp is dim and B+ is back up.
A little background about the build. This is built into my test chassis. I have built several amps in this chassis. The PT is the unit that Mr Hoffman sells as a replacement for the bassman / super reverb. I built a new board for this test. I copied the fender layout except the 68K resistors are on the input jacks and I have 470 screen resistors on the board. The heater string uses two 100ohm resistors and follows the modern convention. The OT is a vintage unit (from a radio) that I got from a member here. I have not used the OT before.
I quickly checked all the connections to the 6V6 tube sockets and found no errors. I have questioned the OT. Can an OT malfunction in a way that would pull the B+ down? Are there any other suggestions for things to check?
Thanks
SLW
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I just finished building a 5E9A. I put the 5Y3 in it and powered it up using a lamp limiter. It looked good. I measured 420VDC. I put the rest of the tubes in and powered it up again. This time the lamp glowed. I measured 300VDC. I started pulling tubes and measuring. With the two 6V6's pulled and all of the preamp tubes installed the lamp is dim and B+ is back up.
That's perfectly normal operation when you have a light bulb (big resistor) in series with the amp. Time to put the limiter under the bench and plug straight into the wall.
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I will do it and report back.
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It works great. I just spent thirty minutes playing it. :icon_biggrin: Thanks for kicking me along. What I was seeing makes perfect sense when I stop and think about it. I guess I am still very conservative with tube amps. I am nervous about burning up a transformer. When I tinker with electronics and blow up a ten cent part I don't think twice about throwing it away.