Had a 400 dropped off for a Restoration, by another AK'er. I normally don't do outside work, but this one intrigued me. Later model 400
SERIAL # 64,746W. Cosmetics (front panel) 8.5 to 9 of 10. Slight streaking of Upper chassis surface.
Owner wants a rebuild to as stock original as I can get it. He understands the upgrades that I do will help it stay in running condition longer and approves. Sooooo.......Gonna do a STOCK rebuild, adding Screen resistors, Cathode resistors, Change Grids to 200K and caps to .1uf. Dave's improved Bal/Bias adjustment but mounted internal (he wants it to look original on top....sorry Dave), all resistors replaced will be vishay or KOA 1% metal film resistors especially to the P.I. so the adjustments hopefully will stay put and accurate.
I asked Hayseed Hamfest to bump up the capacitance to the 1st stage of the Voltage Doubler (Single Cap Can) from 100uf to 220uf to balance the V.D. It's worked well in the one I did last year. Bias P.S. caps will be 4700uf /50V. Will be disconnecting the TAPE/Aux RCA's from each other.
Output coupling caps will be EROFOIL II .1uf 400V and 1000V. These are tested NOS from Apple Scruff and direct from FISHER Plant #2. The rest will be a mix of CD DMT's, DPP, DME's, Wima's, Kemet (X-Y), and K-73's or 42's. I think I can do that with these caps.Will be testing beforeand after each stage for SQ. He wants as close to the original sound as possible, and I share that feeling. So stock it is. I will be testing the current crop of EROFOIL's in it and if they test good, they will stay.
All tubes are FISHER Branded MULLARDS, except for 1 Fisher Branded TELE 12ax7, and one Bogen branded 12AX7. OUTPUT's are FISHER Branded Sylvania or RCA TOP NIPPLE tubes. Lettering is worn off enough I can't tell the EIA Manufacturers code. Yes I tried breathing on it and all it did was sigh......:scratch2:
One of the Mullard 12ax7's broke in transit to the owners house, and another cracked on way here. So to get it up and running (I had one 12ax7 in house), I put all the remaining mullards in the amp, and the Tele as V102. Used a Fisher Branded 12AT7 in V100 and a Known Good RCA Gray plate in V101.
Brought it up on the DBT @100W. no shorts, or smoke. Now for Wall voltage. Started up fine. Been running non stop for a little over 2 hours with temp checks every ten minutes.
Tuning needs a little tweak to align the pointer with the dial. Also pointer wasn't lined up with ZERO mark when turned to full anticlockwise (bottom of scale). This was fixed and dial is closer but still off a little. Low end is about 1/2mHz off, and top end is close to 1mHz off after pointer lined up. Reception on a dipole is very good. Stereo Separation is also very good. The typical cuprits will be addressed here. DeEmphasis (stereo) is off a bit and you can hear it(hiss is almost unbearable in stereo even on strong station). Mono De-Emphasis is good but could be even better. New resistors of the correct value should take care of it.
Gotta go get some batteries for my camera. So Pics will be coming in the next day or two.
Larry
SERIAL # 64,746W. Cosmetics (front panel) 8.5 to 9 of 10. Slight streaking of Upper chassis surface.
Owner wants a rebuild to as stock original as I can get it. He understands the upgrades that I do will help it stay in running condition longer and approves. Sooooo.......Gonna do a STOCK rebuild, adding Screen resistors, Cathode resistors, Change Grids to 200K and caps to .1uf. Dave's improved Bal/Bias adjustment but mounted internal (he wants it to look original on top....sorry Dave), all resistors replaced will be vishay or KOA 1% metal film resistors especially to the P.I. so the adjustments hopefully will stay put and accurate.
I asked Hayseed Hamfest to bump up the capacitance to the 1st stage of the Voltage Doubler (Single Cap Can) from 100uf to 220uf to balance the V.D. It's worked well in the one I did last year. Bias P.S. caps will be 4700uf /50V. Will be disconnecting the TAPE/Aux RCA's from each other.
Output coupling caps will be EROFOIL II .1uf 400V and 1000V. These are tested NOS from Apple Scruff and direct from FISHER Plant #2. The rest will be a mix of CD DMT's, DPP, DME's, Wima's, Kemet (X-Y), and K-73's or 42's. I think I can do that with these caps.Will be testing beforeand after each stage for SQ. He wants as close to the original sound as possible, and I share that feeling. So stock it is. I will be testing the current crop of EROFOIL's in it and if they test good, they will stay.
All tubes are FISHER Branded MULLARDS, except for 1 Fisher Branded TELE 12ax7, and one Bogen branded 12AX7. OUTPUT's are FISHER Branded Sylvania or RCA TOP NIPPLE tubes. Lettering is worn off enough I can't tell the EIA Manufacturers code. Yes I tried breathing on it and all it did was sigh......:scratch2:
One of the Mullard 12ax7's broke in transit to the owners house, and another cracked on way here. So to get it up and running (I had one 12ax7 in house), I put all the remaining mullards in the amp, and the Tele as V102. Used a Fisher Branded 12AT7 in V100 and a Known Good RCA Gray plate in V101.
Brought it up on the DBT @100W. no shorts, or smoke. Now for Wall voltage. Started up fine. Been running non stop for a little over 2 hours with temp checks every ten minutes.
Tuning needs a little tweak to align the pointer with the dial. Also pointer wasn't lined up with ZERO mark when turned to full anticlockwise (bottom of scale). This was fixed and dial is closer but still off a little. Low end is about 1/2mHz off, and top end is close to 1mHz off after pointer lined up. Reception on a dipole is very good. Stereo Separation is also very good. The typical cuprits will be addressed here. DeEmphasis (stereo) is off a bit and you can hear it(hiss is almost unbearable in stereo even on strong station). Mono De-Emphasis is good but could be even better. New resistors of the correct value should take care of it.
Gotta go get some batteries for my camera. So Pics will be coming in the next day or two.
Larry