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74 Custom 100 with only 451DCV on the plates???
Posted: Fri Aug 06, 2010 7:16 pm
by clusterstudios
I was was checking out a 74 DR103 today. Nice amp but when I went to check the plate voltage (or B+) I measured a suprising 451DCV
Most other Hiwatts I've measured all read around 500-5115DVC. What can be wrong with this one?? The caps are good with no hum. Could this be a bum PT from the factory just like the Marshall ones from the mid 70's??? Any comments would be appreciated. Thanks.
Joseph
Re: 74 Custom 100 with only 451DCV on the plates???
Posted: Sat Aug 07, 2010 2:49 am
by clusterstudios
Anybody there???
Re: 74 Custom 100 with only 451DCV on the plates???
Posted: Sat Aug 07, 2010 7:01 am
by mikhailwatt
What was the mains voltage?
I think the spec was 460vdc plate, but you start hitting 490+ running them off modern 120-125vac on the 115v tap.
My 1980 DR504 runs about 450-460 (if I recall) with the mains knocked down to 114vac on the 115v tap.
Re: 74 Custom 100 with only 451DCV on the plates???
Posted: Sat Aug 07, 2010 12:22 pm
by clusterstudios
460DCV is common to the 50 watters but not the 100s. It's the 1st time I've seen it on a 100 watter.
Re: 74 Custom 100 with only 451DCV on the plates???
Posted: Sat Aug 07, 2010 3:54 pm
by mhuss
What are your mains vs. "voltage selector" voltages? The Biacrowns I've seen run silly high voltages (500+) when fed modern US mains, but the older Hylights not quite so much (unless you're feeding a 115v tap 127 volts).
--mark
Re: 74 Custom 100 with only 451DCV on the plates???
Posted: Sat Aug 07, 2010 4:39 pm
by philmanatee
My 83 Biacrown DR- 504 is 517v B+. Phil
Re: 74 Custom 100 with only 451DCV on the plates???
Posted: Sat Aug 07, 2010 4:48 pm
by mcdyas
my 1972 dr103 is around 476. is there a "normal" reading that should be expected?
Re: 74 Custom 100 with only 451DCV on the plates???
Posted: Sat Aug 07, 2010 7:04 pm
by clusterstudios
philmanatee wrote:My 83 Biacrown DR- 504 is 517v B+. Phil
That's more like it. I'm in Toronto using 120AC.
Re: 74 Custom 100 with only 451DCV on the plates???
Posted: Mon Apr 04, 2011 10:34 pm
by stokekt88s
is it possible it has a 50watt transformer in it? check the tranny codes is worth a look. a friend of mine blew his 100 tranny and replaced with a 50, god knows why? but it worked, to a fashion. just a thought......