Quote:
Originally Posted by buggies
Just as confirmation, this from a Heathkit parts list of transformers extracted from the pdf available at:-
https://w5rkl.com/wp-content/uploads...ifications.pdf
54-2-24 Power Transformer (P: 115/230V; S: 130V@10mA, 6.3V@800mA)
Used on IM-28, IM-38, IM-5228, IT-7400 |
Thank you for that information which confirms that the transformer is rated for UK mains operation. I have saved a copy of that document for future reference.
Quote:
Originally Posted by ColinTheAmpMan1
Yes, the equivalent capacitor in the V-7A is 0.01uF at 1600 V. If you just want to see if the VTVM works, and you aren't going to put a signal above a few volts into it, then I don't think you need to bother about the capacitance value too much and that a cap with a couple of hundred volts rating will do. I was hoping that I might find a suitable replacement to give you in my collection, but regrettably not.
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Thank you for having a look. I had another look and found a ceramic cap 103 (10n) @ 2kv. While a ceramic cap is not ideal due to its microphonic properties and thermal characteristics which might cause problems, it was sufficient for power on test purposes. I have, of course, replaced all of the other paper caps as well.
Quote:
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Ok, so if you don't have a Variac but do have a step-down transformer, why not try powering it up with the transformer first? if the heaters look to be glowing right and the heater voltage is 6.3 VAC, then it is a 120 V model and no harm has been done.
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I has enough time to do a quick power on test at 120v. The voltage measured across the DC smoothing cap was about 80v (well short of 120v) and across the heater the AVO read about 3vAC, so half of what it should be. Strangely the valves did seem to operate as I could get a DC reading on the scale, but the reading was only about half of what it should have been. All (including the data from buggies) would seem to indicate that this unit is indeed configured for 240v. I will do some further testing, including at UK mains voltage tomorrow.
I should have looked at the voltage range of the meter. The highest range is 1500v, so C1 no doubt needs to be rated to carry at least that voltage. I will have a look around for a suitable cap. Thanks.