Clueless Idiots and High Voltage Vacuum Tubes Really Do Mix!

Paleo-Electronics header image 4

Entries from March 31st, 2011

Debugging the Medalist – F#%$!!

March 31st, 2011 · No Comments · Amp Repair, Medalist Debug

Ok. When last we met (do I say that every time?), we had decided that the power caps were bad. At least C4A and since those crap cans go bad all the time, I decided to go for them all. First lets have a go at the schematic with test points marked in. One thing […]

[


Debugging the Medalist – Power Supply Filtering

March 28th, 2011 · 2 Comments · Amp Repair, Medalist Debug

As you might recall from two posts ago (“Scoping the Power Supply”) we were unable even to scope the power supply ripple at TP3 and saw a hideous deformed thing at TP5. The lack of filtering certainly indicates that C4A (the 20μF from the cap can) was blown. Since that big funky cap can itself […]

[

Tags: ··········

Sidebar : Rectification and Filtering

March 28th, 2011 · No Comments · Amp Repair, calculations, Medalist Debug

Here is a nice little explanation of rectification and smoothing. Here is one that focuses on smoothing. This and most amps have full wave rectifiers. Our 6X4 tube is a twin diode and the PT is has a center tap on the secondary. Fun fact : The first vacuum tube was a diode. Triode is […]

[


Debugging the Medalist – Scoping the Power Supply

March 27th, 2011 · No Comments · Uncategorized

Last time, we took some DMM measurements of the power section. Some odd numbers and all made me think about it and I even called a physicist friend to ensure that I understood the readings I was getting. He suggested I had better check the DMM. I switched to another one, but I also swapped […]

[


Debugging the Medalist – Hot Measurements and the Power Supply.

March 27th, 2011 · 1 Comment · Amp Repair, Medalist Debug

All the previous measurements were taken with the power off (and disconnected). Now it’s time to measure some voltages. Before we do that however we should talk a bit about the set up. You are going to want two fairly big resistors. These are very small amps (this one should put out about 5 watts […]

[


Debugging the Medalist – Part I

March 26th, 2011 · No Comments · Amp Repair, Medalist Debug

Allriiiighty then! Time get inside the Medalist and see whats up. First, the seller reported low output and loud hum. Amp is in great shape for a 44 year old amp, only the grill cloth is obviously deteriorating. Original schematic stapled inside will be a lifesaver. The only other thing of interest on the outside […]

[

Tags: ····

Now on the bench : A 67 GA-5T ‘Medalist’ Skylark

March 26th, 2011 · No Comments · Amp Repair, ebay, Uncategorized

Preamble When last we met I claimed, without evidence, that I was in possession of an authentic, original schematic for a 67 GA-5T Skylark. How could I guarantee such a thing? I took the schematic out of a 67 myself! I just bought one on ebay after all the doings with Patrick and trying to […]

[

Tags: ········

Oh what a find! GA-5T Skylark ‘Medalist’ schematic!

March 22nd, 2011 · No Comments · Amp mods, Amp Repair, Schematics

Ok. I can guarantee that this is the schematic for a ’67 or later GA-5T. This is commonly called the ‘Medalist’ styling and an example with some info is found at John Kings site. How can I guarantee that? I’ll get to that later, but for now, trust me. Full size file is almost 3 […]

[

Tags: ···