Idoia wrote:Me again,
I am sorry but I cannot find ANY Rel-Cap polypropylene 0.15uF 450V and 0.02uF or 0.022uF 600V. I had checked the links you gave me already Greg and they don' t do them. Can I replace them with Mallory, AudiCap or Multicap with the same values ?

Yes. You can also try the single wind polystyrene and foil caps they sell at those values. It is just one of those audio-file choices that people geek out on, but in all likelihood, wont be pivotal.

Also the electrolytic ones, I can find some Sprague-Atom or Vishay-Sprague with the needed values but none operating above 85 degrees. Will that be okay if I use them or should I priviledge 105 degree caps to them regardless of the brand ? I have found some Nichicon Snap-In Aluminum Electrolytic Capacitors, will they do ?
Alex

You should try to get 105 degree caps if you can. The 85 degree ones will work, but not as long.

Hey Greg,
I found some panasonic EB and TS-ED 105degree for those value and I tried to edit my post but you replied at the same time .

The last one, I promise: You said that we should round up to the next standard value, I need a 4000uF 20V cap and there is 4700uF 20V but there is also 3900uF, should I go for the 4700uF anyway ?

Thanks
Alex

Idoia wrote:Hey Greg,
The last one, I promise: You said that we should round up to the next standard value, I need a 4000uF 20V cap and there is 4700uF 20V but there is also 3900uF, should I go for the 4700uF anyway ?

Yes.

Hi Greg,
I am doing your modif for a preamp that I will mainly use in Europe. I have to change the input voltage of the device.
I have two solutions:
Either I change the transformer and I found one that can output the voltages needed inside the preamp (which I am not sure about).
Or I can insert a step down transformer that goes from 220V to 110V just before the main one. That seems to be the easiest.
What I need to know is how many Watt should the step down transformer provide. I have tried to make it work with a travel adapter that ouput only 45W but it does not seem to be enough.
Thanks
Alex

I updated the schematic link. Note the changes on the first post.
Good luck!

Idoia wrote:Hi Greg,
I am doing your modif for a preamp that I will mainly use in Europe. I have to change the input voltage of the device.
I have two solutions:
Either I change the transformer and I found one that can output the voltages needed inside the preamp (which I am not sure about).
Or I can insert a step down transformer that goes from 220V to 110V just before the main one. That seems to be the easiest.
What I need to know is how many Watt should the step down transformer provide. I have tried to make it work with a travel adapter that ouput only 45W but it does not seem to be enough.
Thanks
Alex

Don't change the transformer out if you are not sure of what you are doing! Try to get someone to help you with that.
I am not certain on the exact current consumption of the 351s. A 45W commercial stepdown transformer should be big enough though. See if it gets warm to the touch.

Hi greg,
I have put another transformer before the main one so that the current is transform into 110 before. The only thing is that the transformer should at least provide 100W unless the ampex won't power up.
I have done two of this units and have for both of them the same problem:
Looking at your schematics, on the amplification board, the middle one, I got all voltages right.
On the record one however, I get 13.5V between R25 and R28 and 15.4V between 4 and 5 of V1.
I triple checked all resistors and cap values and got them matching your schematics. Is there a slightly chance there are still an error on the schematcis ? For ex on the photos you gave us, I can see that you kept the original R60 which is on the original schematics 3ohms. On the modification schematics you put 1.5 ohms. I might be wrong but at this level this makes some difference, no ?
Has anyone here tried to do this modification appart from myself ?
I'd really like some help here.
thanks.
Alex

Maybe one question that could really help me, on your schematics, both 9 pin of V5 and V4 are connected together with the GN/Y of the main transformer. Am I reading well ?

Least but not last, on the same part of the board, pin 5 of V5 is connected to pin 4 of V4 but on the original board, both pin 5 of V5 and V4 are connected to eachother, which one is it ?

I know you have done this long time ago but unless you match this against one of your device I have little chance to find the correct way to connect those tubes.

Thanks a lot Greg.
Alex

rambi10 wrote:Hi Greg

I got twelve AMPEX 351 preamp and i want to transform it into a mic preamp.
I saw on the electrical audio forum that you already did this kind of thing.
I would like to know if you have a complete wiring scheme because it's too difficult to wire only from the forum's pictures, I can't get all the wiring's details.
I already cleaned everything and took out the tube sockets and caps like
C1,C2 and C10 on the first PCB(layout).
I will change all the components you suggested on the forum like the resistors, caps and tube sockets.
In fact, the hardest for me is the wiring between the transformers,the switches, the pots and the IN and OUT XLR's.
Do you have any tips to help me out ?

Thanks in advance

Aurelien RAMBACH
RETENTIVE SOUND AGENCY
49 boulevard du lycée
PARIS
FRANCE

If you want, call me at 0155959820 or m

I moved you to the right topic.
I don't have a wiring diagram other than the schematic, which you can see the updates on this thread. There are some drawings that the last tech made for wiring in some of the peripheral components, but they are irrelevant and would be confusing to you now.
What is troubling you about wiring the in/out and the transformers?