On Apr 29, 1:07*pm, "Dave M" wrote:
Meat Plow wrote:
On Fri, 30 Apr 2010 01:49:05 +1000, Phil Allison wrote:

"Meat Plow"

What's the URL of the schematic?

**See:

http://recordist.com/ampex/schematic...n/601schem.gif

** Wanna bet the mic input tranny is missing and /or the hum balance
trim pot is burnt out ?

How is the OP is recording, from Line or MIC? Don't remember and you
snipped the quote.

Hum balance is R-147?

OP says that the hum is present when recording from both mic and line
inputs. *Sounds like a ground connection is broken somewhere around V101,
V102 or V103. *Also check those tubes for heater-cathode short. *Check line
record level pot and mic record level pot for broken grround connection or
open wiper.
Make sure that the bias oscillator (V103B) is running in record mode.
--
David
dgminala at mediacombb dot net

I once had a bias oscillator kick up to a very high frequency [part
failure] intermittently. You could not believe the high quality of
the recording when the oscillator went berzerk. Down side, got super
hot, even the plate on one tube just starting to glow.