Help, no bias voltage

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danman
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Re: Help, no bias voltage

Post by danman » Sun Sep 04, 2016 9:42 am

Caps are pretty robust and you rarely see a new one that is bad, but...being that the choke was hooked to ground, it is possible that you may have damaged one during the initial power up. You could start to unsolder them, working your way backwards through the supply to see which one is blowing the fuse. I would also check for any solder bridges, misplaced jumpers or anything else in the power supply that would cause a short. A quick check of the choke wouldn't hurt either to be sure that it was not damaged while it was hooked up to ground. It may also be beneficial to disconnect the bias supply from the power supply at the 27k (no power tubes installed though) to eliminate that circuit as a potential problem. If the fuse holds with the bias disconnected, you know where to look next.

Are you using a light bulb limiter during your troubleshooting phase? It would save you alot of fuses and allow you to at least power up the amp long enough to get some voltage readings throughout the power supply and possibly find your short.

sixpakldp
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Re: Help, no bias voltage

Post by sixpakldp » Sun Sep 04, 2016 11:59 am

Figured out that issue, had the bus wire also around 27 k resistor lug. Voltages are within spec, power tunes in and bias. Plugged in and I get a high pitched squeal. Going to recheck the pre amp section. At this rate probably another wiring mistake.

danman
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Re: Help, no bias voltage

Post by danman » Sun Sep 04, 2016 2:10 pm

High pitched squeal usually indicates that the OT primary wires need to be reversed at the power tube sockets. If temporarily disconnecting the purple nfb wire from the impedence selector stops the squealing, then you will need to reverse the primaries. Lifting the NFB is a quick way of checking the primaries. Hopefully you have enough slack in the wires to reverse their connection points at pin 3. Good luck!

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neikeel
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Re: Help, no bias voltage

Post by neikeel » Sun Sep 04, 2016 4:17 pm

danman wrote:High pitched squeal usually indicates that the OT primary wires need to be reversed at the power tube sockets. If temporarily disconnecting the purple nfb wire from the impedence selector stops the squealing, then you will need to reverse the primaries. Lifting the NFB is a quick way of checking the primaries. Hopefully you have enough slack in the wires to reverse their connection points at pin 3. Good luck!


:thumbsup:
Neil

sixpakldp
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Re: Help, no bias voltage

Post by sixpakldp » Mon Sep 05, 2016 12:36 pm

Thanks guys. Got it all sorted out and working again. I had some wiring mistakes but got them worked out and got it fired back up. I tore it down to get the build cleaner than my first pass many years ago and to swap in some Iskras and a few pihers. I also removed the fx loop and lar mar. I've never played this amp without any mods and now that I have a tweed deluxe and a deluxe reverb this amp doesn't need to be as versatile as it was when it was my only amp. Really sounds great. I like the bare bones approach. I think I got cocky and had a few mistakes. One thing I can say is no matter how many times I've experimented on this amp and have feared it's been toast, it's always a mistake on my end and the amp always bounces back. Just goes to show how good the metro/heyboer trannies are and what kind of abuse they can handle (unintentional of course). Thanks again, case closed!

danman
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Re: Help, no bias voltage

Post by danman » Mon Sep 05, 2016 12:47 pm

Good to hear!!

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