Ampex 351-2 restoration project

yup.

Very nicely bookmatched! I should know the wood, but I have to ask.

beautiful.

Hi Folks: Hope all of you are well. The same friend who gave me my first Ampex 350 gave me a second one (!) and I want to do the same restoration using GAS PCBs. The problem is that Recording With GAS seems to be MIA -- no web site and no response to messages via FB or Gearspace going on two years. If anyone has a set of PCBs (power, record, and repro) that they don't need, please send a message! Thanks, Steve

I'm rebuilding half a dozen Ampex tape recorders, refitting a recording studio. I'm having huge issues with the female spade connectors of the 351 boards; it's actually a major problem. They are loose, corroded and break at the slightest pressure. I know they are similar to a Faston, but they are female and slide over the edge paths. Anyone working on one of these will see this problem. Does anybody make these little gems anymore or is this a complete hardwire job I'm facing? Thanks for any help!

Was able to do some slight bending and crimping with 4.8mm fastons and they'll work great in a pinch. The orginals were incredibly thin and I'll probably hardwire the connections in the future. By the way, I've rebuilt just about everything on the first of these units, including the balanced capstan -bushing bearing motor with low clearance bearings. What a great design; quiet and smooth. By the time I get done with about 10 of these, I should know all the tricks.

Here's a photo of Pink Floyd in a Decca studio with an Ampex MR70 in the background. The MR70 is arguably the finest sounding tape recorder ever made, in my semi-humble opinion.

Hello,
I would recommend sending an email to Dave Dintenfass at: www.fulltrackproductions.com he is extremely knowledgeable about anything Ampex.
Good luck with your project!

Hello,
Welcome to Polk's forum! It's been a while since I refurbished my Ampex 351, but I'll try and answer your questions.
Q: The face plate is filthy. What did you all use to clean it? Is it aluminum?
A: I used Flitz metal polish and soft cotton balls to clean the faceplate. However if the faceplate is heavily scratched they can be resurfaced or "skimmed". This is a process where a very thin section of the metal's surface is planed away. Since the lettering is embossed into the metal rather than printed on top it is not harmed. This should be done by a skilled metal shop and the faceplate will have slightly different length and width since the process will very slightly flatten the metal.
Q: My old unit had the green(ish) boards, and this "new" one has the blue boards. What are the implications? Is one better than the other? I imagine they are from different eras? Are the green boards from older?
A: I've only had experience with three units and most have a mixture of tan and blue boards. I don't know of any differences.
Q: This "new" unit has a more gold/copper/bronze looking chassis, while my old unit was dirty gray. This "new" unit as weird trap door on the undercarriage of the unit. As far as I can remember, my old unit did not have this door.
A: Yes, I've noticed different chassis colors and attribute it to differences in production years. All of the one's I've had have the access panel on the bottom. Keep in mind the 351 has a small dot on the front faceplate under the VU meter denoting it to be a 351 as opposed to a 350 which has no dot.
Q: 4. If I'm to try to build a diode rectifier to replace the og selenium rectifier, to I need to follow it with any sort of resistor to compensate for the higher output voltage?
A: Yes, the silicon rectifier will have a lower internal resistance than a selenium based version resulting in a higher DC voltage going to the filaments of the tubes. Here is a schematic:

To compensate for this 3R-60 will have to be increased to give the same 12.6vdc to the tubes. Is your unit functioning? If so place a DC voltmeter across 3R-60 and measure the voltage drop across this resistor. Then with the unit switched off remove one leg of 3R-60 and measure its actual resistance. Then take the voltage drop you measured and divide it by the resistance you measured. This will give the amount of the current flow drawn by the tubes. Then go ahead and change out 6CR-1 selenium bridge for your chosen silicon version and replace 3R-60 and measure the DC voltage at the point shown on the schematic. Let me know what you find.
Cheers!