mikeydee Posted August 11, 2014 Share Posted August 11, 2014 I bought an old OBT pre amp board from obbm to create a little pre amp module. I have it working fine with the input ht set to 240vdc giving a plate voltage of about 140 on v1a. I would be keen to hear from any one that knows what the ht should actually be. And, if anyone has a schematic that would also be very welcome. Mike Quote Link to comment Share on other sites More sharing options...
Bigwan Posted August 11, 2014 Share Posted August 11, 2014 Your wish is my command! PM me your email. Quote Link to comment Share on other sites More sharing options...
mikeydee Posted August 11, 2014 Author Share Posted August 11, 2014 Done Quote Link to comment Share on other sites More sharing options...
mikeydee Posted August 12, 2014 Author Share Posted August 12, 2014 Just in case anyone was anxioustto know, it turns out the high voltage supply to the pre amp is 175v. Quote Link to comment Share on other sites More sharing options...
Subthumper Posted August 19, 2014 Share Posted August 19, 2014 That would probably explain why they overdrive so easily. The less voltage the browner the sound. That's quite low compared to a lot of other amps using the same valve. Or is that the voltage on the actual plate of the valve as opposed to the HT supply? Quote Link to comment Share on other sites More sharing options...
mikeydee Posted August 19, 2014 Author Share Posted August 19, 2014 Yes I was expecting something in the range of 150-250 volts. The 175v is what is supplied to the HV connector on the input board. There are a couple of 10k dropper resistors one for V2 and a further one for V1 so the plate voltage on V1 is reduced a fair bit once biased up. I'll post measurements if folks are interested. See you are in Bristol too - so a local Hi to Subthumper. Quote Link to comment Share on other sites More sharing options...
Subthumper Posted August 21, 2014 Share Posted August 21, 2014 A Bristol hello to you too. I don't have the otb schematic but I do have the ad200. I'm sure that runs at least 100volts plus,more than the terror. Would be interesting to compare the two and see if the otb is improved if run at a higher voltage. Quote Link to comment Share on other sites More sharing options...
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