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Post by mauro on Sept 17, 2018 0:11:37 GMT
Greetings to all forum members,
I have an amplifier from a model G that was given to me and I'm thinking of rebuilding it as a spare for my G.
It is missing the volume control and has a replacement power transformer and choke that appears to be taken from an old television chassis but bolts in perfectly.
The problem is the unloaded voltages seem a bit higher than normal but I was thinking if I ran only 6L6GC's the voltage might be ok.
High voltage 870vac
Heater voltage 5.8vac
These are unloaded voltages, no tubes installed.
Just wanted to get the opinion of the members here before I move forward.
What do you think?
Thanks, Mauro
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Post by robnyc on Sept 17, 2018 1:47:18 GMT
Mauro, I've used trans from RCA 1967 color sets and an old Bogen amp. What counts here is the rectified-filtered potential on the tube plates. 10%+ Higher is NBD.
The heater @ 5.8 is a bit low and this can make marginal tubes sag into reject territory. Since the amp normally gets heater from the main tran this doesn't matter here.
Many of my amps are cobbled together this way and all are working well.
RobNYC
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Post by Ron Rich on Sept 17, 2018 13:37:58 GMT
Guyz
--RTFM !! Heater voltage for all but the 5U4 tube, comes from the WSR transformer, and should be 5.8 VAC, not 6 volts ! As for the other values--10% +- should be OK--Ron Rich
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Post by mauro on Sept 17, 2018 21:32:05 GMT
Guys,
5.8 is the heater voltage for the 5U4 rectifier, other amps I've measured 5.4v. Not a big deal here but the HV measures 870v where other amps measure 760v.
This is the one I'm worried about.
It's about 14% high and I think it should be ok but wanted the groups opinion.
Thanks,
Mauro
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Post by robnyc on Sept 17, 2018 22:32:25 GMT
Guyz --RTFM !! Heater voltage for all but the 5U4 tube, comes from the WSR transformer, and should be 5.8 VAC, not 6 volts ! As for the other values--10% +- should be OK--Ron Rich Ron, 6.3 is the design center for -all- tubes with a "6" as first digit or "E" (Europe). Seeburg spec's 6.1 from their main tran. 5.8 Is IME marginal. As tubes age the cathodes lose emission due to depletion and impurities forming on the surface. This requires greater heat to keep the conduction up. Try this, on your tube tester select a worn tube and reduce the heater voltage by 10%. You'll see the needle begin to trend downward. On a weak tube, try increasing heater by 10% you'll see an increase on all but tubes too far gone. RobNYC |
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Post by Ron Rich on Sept 18, 2018 2:47:07 GMT
Hi Rob,
You are correct--I miss read the schematic on the WSR-7 -- The winding above the 6.1 is 5.8--
Ron Rich
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