Ampex 601 Reel to Reel plays back fine but has only AC hum in record mode
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From: mark on 29 Apr 2010 09:03 The input section has severe AC hum when recording via the Microphone & direct line but playback through the output & headphone jacks is fine. If anybody is familiar with working on these any help with listing the usual high failure suspects & what parts should be upgraded would be greatly appreciated. I just moved & misplaced my ESR tester so I'll definitely need to find it to test all the old caps in this one some of which obviously need to be replaced. I tried printing out the schematic off the net but for some reason my computer (Powerbook G4) wouldn't print it. I repaired TVs/VCRs/stereos for 35 years but not many vintage tube audio units. Thanks, Mark
From: Phil Allison on 29 Apr 2010 11:49 "Meat Plow" > > What's the URL of the schematic? **See: http://recordist.com/ampex/schematics/601man/601schem.gif ** Wanna bet the mic input tranny is missing and /or the hum balance trim pot is burnt out ? .... Phil
From: Dave M on 29 Apr 2010 16:07 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/schematics/601man/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
From: Robert Macy on 30 Apr 2010 11:47
On Apr 29, 1:07 pm, "Dave M" <dgminala4...(a)mediacombb.net> 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/schematics/601man/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. |