Paleo-Electronics

Clueless Idiots and High Voltage Vacuum Tubes Really Do Mix!

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Entries from April 23rd, 2011

Debugging the Medalist – More Weirdness

April 23rd, 2011 · No Comments · Amp Repair, calculations, Medalist Debug

So I replaced the bad resistors and took so measurements. Basically, everything looks perfectly reasonable, and it sounds great at low volumes, but I have one major problem. Anywhere past 3 or 4 on the volume knob slams the output tube with up to 30 V (rms) on the grid! For reasons I may show, […]

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Debugging The Medalist – The Output Tranny

April 7th, 2011 · 1 Comment · Amp Repair, calculations, Medalist Debug

Well, the parts have arrived, but first, I want to understand that output section a bit better so let us examine the OT. The always helpful Patrick at Mercury Magnetics suggested that the drop in replacement they make is the GA5-0 which has an 8kΩ primary to 8Ω secondary. He also noted that they varied […]

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Debugging the Medalist – Mistakes Were Made

April 7th, 2011 · No Comments · Uncategorized

As I try to figure out what is wrong without blowing more 6BQ5’s to do it, I have to acknowledge that I rushed a couple of things in my excitement. I guess I’ll never really be a radio man. Whether or not those mistakes caused the failure is not likely to be known. However, those […]

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Debugging the Medalist – Intelligent Design

April 5th, 2011 · No Comments · Amp Repair, calculations, Medalist Debug

As we now have some reference voltages to use (see previous post) we can take a lot of the guesswork out of our debugging. So here is the power section from the Master Service Manual. Those are design values. The test readings are in the top corner of that page (319 in the MSM) and […]

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A Tale of Two Schematics

April 4th, 2011 · No Comments · Amp Repair, calculations, Medalist Debug, Schematics

In the course of working on two different 5T ‘Medalist’ Skylarks, we have come across two different schematics. One of them came from blogfriend Patrick and is found in the 1966 publication of the Gibson Master Service Manual. The other was attached to the amp I bought. Here is the one I got : Here […]

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Debugging the Medalist – What Happened?

April 3rd, 2011 · 1 Comment · Amp Repair, calculations, Medalist Debug

I don’t really know what happened. My suspicion is that the tube blew, but the other possibility is that the cathode resistor blew, causing the tube to blow. Again it could very well be the 44 year old original tube and I might well be the first guy to run it for a long long […]

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