I've been away from the forum for a while, as I was building a new internet machine. But now that I have come back to this delightful thread I would like to say.

THREE CHEERS FOR GREG!

And thanks, too.

Sigh...More Modification Questions...


What type of bridge rectifier should we buy?

What is the miniature switch next to the green lighted one? Is the green light only an indicator? I found one from Newark that is a switch also...


Thanks.

Dan

Oh, and so that I'm not always a "taker," here's a tip:

When removing the old components from the boards, a Dremel moto-tool with a disc cutting attachment makes quick work of all of them. It should save you some major time, since you'll only have to melt the solder on the bottom of the boards and pull out the metal pins from the components (which are now straight because you cut them). Trying to melt, suck, and unbend metal socket pins is a major pain in the ass.

Hope this helps a little...

Dan

I just noticed a typo-

The attenuator is not a Davin but a Daven. Sorry for all you guys trying search engines.

here is some more restoration info....if anyone is interested

http://ampex.hughescatalog.com/

jrod

Sorry Dan. I just noticed this.

What type of bridge rectifier should we buy?

None. Keep the 6x4 tube where it is, and if you want to replace that selenium rectifier (radiator looking thing behind the output tranny) just use two 1N4001 diodes.

What is the miniature switch next to the green lighted one? Is the green light only an indicator? I found one from Newark that is a switch also...

This is the 600 Ohm output termination switch (see schematic). I usually leave it on all the time, but you can switch it in and out to see how it effects the sound.
The green switch does carry audio, and serves as the output attenuator engage switch.

Don't let me get away with saying the word "tranny" again.

I tested a new logarithmic pot for replacing the gain pot. The pot sucked and the gain/rotation relationship was irregular. I'm leaning towards the switched gain option.

Do any of you have an opinion? Pot or Switches?
Keep in mind the output attenuator being like a fader.
I'm thinking for the switch having 12 to 16 positions. The first being "Off" then having gain stages of 5dB.

Okay Greg,

Having just asked a bunch of questions about the MS Matrix project I thought I should ask a few clarifying questions about this one.

First, the output attenuator switch schematic is confusing me. You say that you used a 6P2T switch. Do they even make those? Is that contained within the green lighted switch? And, above the "600 Ohm Term" switch symbol there seems to be something written next to the resister. I can't make it out. What does it say?

Finally, what kind of switch did you use for the -18dB Pad switch. I assume it's a rotary one. Which one was it? How many poles and stops?

Thanks Greg. Hopefully I'll find some way to repay you for all of your help someday...

danmaksym wrote:Okay Greg,
...
First, the output attenuator switch schematic is confusing me. You say that you used a 6P2T switch. Do they even make those?
Is that contained within the green lighted switch? And, above the "600 Ohm Term" switch symbol there seems to be something written next to the resister. I can't make it out. What does it say?

Finally, what kind of switch did you use for the -18dB Pad switch. I assume it's a rotary one. Which one was it? How many poles and stops?

...

They do sell that switch. I believe it was bought from Newark Electronics.
The # next to the resistor is 604 meaning 604 Ohms.
The switch we use for the pad is a Grayhill rotary switch P/N 71BD30-02-2-AJN configured for DPDT operation. You can determine the numbers of stops.
Sorry it took so long to answer this.

Thanks for the info Kevin. I didn't know that about the traces. We haven't had a bass response issue yet. Maybe we inadvertently did our own heat treatment when we cleaned the boards. I don't like the idea of permanently altering the units either, but these particular 351s were on their way to the landfill when we picked them up. Steve caught a bunch of hell from people on the Ampex list when he talked about it.