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Old 07-15-2010, 12:07 PM
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VintagePC VintagePC is offline
Tube bug got me 05/2010
 
Join Date: May 2010
Posts: 535
Ok... been running the set for a while with a CD player. Sound is good (even on the built-in speakers), but there are a few things:

1. Left channel is fainter than the right. Likely a dirty balance or volume pot.

2. There's a faint hum with no audio and the volume on max. This goes away at lower volumes, so it's not of major concern.

3. Power transformer gets hot- still touchable, but not comfortable, kind of like a fresh cup of coffee. Voltages are steady and looking good after ~2h of running.

4. Some sharp audio (e.g. guitar) had a bit of distortion to it- It went away when I fiddled with the tone pot, so I think it is again, a dirty pot.

What is the suggested approach? replace the pots or clean them?

I don't have any deOxit on hand, are there good substitutes? It already got much better just from working the controls for a bit with the set off.

Edit: Just re-probed the radio tube voltages. They start high and eventually come down and stabilize. The 6BE6 is indeed at about 88V, but the 6DC8 is at about 55... well outside a 20% tolerance, if the schematic indeed shows 35V. It's too fuzzy to make out; can someone see whether it is "36" or "56" V? on the 6DC8? This datasheet suggests the tube can handle it (http://tubedata.itchurch.org/sheets/020/e/EBF89.pdf) but it may indicate part of the reason the AM isn't tuning.

Also did a quick check on sweeping the dial, but no stations came in. Could be that there's nothing rolling in yet, but I should at least be able to find the local AM at 1450... but it's possible that rewinding the oscillator bumped it off the top edge of the range.

Last edited by VintagePC; 07-15-2010 at 04:40 PM.
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