37-610 Voltage measurements - Printable Version
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37-610 Voltage measurements - Arizona_steve - 01-05-2014
I'm restoring a Philco 37-610. I've replaced the larger 'lytics & have measured pin voltages, finding most to be close to the published specs, BUT the 6Q7 plate is at 208 Vs. 125!!! I certainly agree W/ Ron in regards the use of modern digital voltmeters rather than the low impedance equipment available back in the '30's... I have done some preliminary resistance measurements and found nothing pointing to such a high plate voltage. The 6A8 plate is near normal, being fed from a point near where the 6Q7 gets its' B+...
Has anyone out there seen this situation? I would appreciate it if someone having a working 37-610 would post their actual voltage measurements, or perhaps point me in the right direction. The set will tune a local station, albeit at fairly low volume. I'm lining up a source for the various small value caps & will begin to replace same, but like a former New Englander would venture: "If it ain't broke, don't fix it..."
RE: 37-610 Voltage measurements - BrendaAnnD - 01-05-2014
Too high a plate voltage usually points to either a dead tube, or an open or high impedence cathode circuit. Since the cathode on your 6Q7 is tied directly to ground, that almost leaves the tube itself as the culprit. That's the only thing I can see in that schematic.
RE: 37-610 Voltage measurements - klondike98 - 01-05-2014
Welcome to the Phorum! Lots of good folks here to help you out. All the paper caps including those bakelite block caps need to be replaced even if the radio is working now. The bakelites are not that hard to rebuild: see the info here http://www.philcoradio.com/tech/blocks.htm and http://www.philcorepairbench.com/capbuild.htm
RE: 37-610 Voltage measurements - Arizona_steve - 01-12-2014
DUH!!!
Having looked at the Riders Vs. Philco service info, it appears that I suspected a really high plate voltage on the 6Q7... Riders appears to spec "125"; Philco appears to spec 175. Conclusion: at 208 Volts it is just high, not REALLY HIGH... (AND would no doubt look even closer if I had the 1000 Ohm/Volt Philco 025 test instrument). Would someone look at their paperwork and confirm? Now onto recapping, just waiting for my recap kit to come in. Stay tuned.
RE: 37-610 Voltage measurements - morzh - 01-12-2014
Steve
It is all great and I am glad that your voltages are close to where they should be, but personally I prefer completing the recap/recarb first, check the tubes, and then do the voltages. This will take of a load of questions off your mind.
Plus it is safer. If a cap is not an electrolytic, it does not mean that it cannot short the supply.