RCA Reel to Reel Conversion??

[rdshear]

I had aquired many years ago an old RCA reel to reel. Now, at age 45 I'm wanting to learn guitar and being that I've always been an electronics type guy thought that, that old tape recorder might make for a good fender champ type conversion.

It has 4 tubes, a 6x4 rectifier, a 5879 that I think is used for bias in recording, a 12AX7, and a 6AQ5 output tube. I have stripped the amp from the recorder and it will function as is if I apply a signal on the wires from the old head. I connected an mp3 player to those and got audio through the speakers.

I have since stripped most all the components figuring that I'll have to start from scratch. I do have a few questions though.

1) The recorder had an external speaker connection that disconnects the internal speakers when one is plugged in. According to the manual, it states the external speaker impedence should be 3.2 ohms. Would a 4 or 8 ohm speaker be ok with that output transformer or would I have to find a 3.2 ohm??

2) Would the 6x4 rectifier tube be ok or should it be swapped out for diodes or a different rectifier tube?

3) Being that the amp "worked" as it is, would I be able to re-use the old capacitors or should I just replace them from the start?

Most of my electronics experiance has been in the digital world and I'm not familiar with much analog circuitry, let alone that from 60 years ago
Any help or thoughts on this would be greatly appreciated.

Rick

[Ian444]

A 4 ohm speaker should work fine. If the 6x4 delivers the required current, I would leave it in there. Diodes will give a higher B+. Usually the worry is with old electrolytics (I have read), there probably isn't many in there, so changing them is up to you. Sounds like a fun project.

[rdshear]

I know the recorder audio had little noticable hum when it was intact so I am guessing that while old, the caps may still be good. However, I plan to replace most of them anyway. The main one I was considering keeping is the metal canned one that is soldered to the frame. This houses a 50 and a 30 uf cap in the one can. This is the first cap after the rectifier on it's outputs.

I've seen a few champ type circuits on the web, some of which use a 6aq5. Are there any that are better than another that you would maybe recommend?

I'm trying to keep the cost to a minimum, since this is going to be my 1st tube circuit ever, my chances of something not working as expected is probably high

Rick

[Miniwatt]

Oh that's cool, I'm planning a Champ clone myself
A 6x4 works fine and is a sweet tube for hifi, never saw it in a guitar amp.

[Ian444]

It's possible the 6AQ5 you already have is as good as any. If it failed and I lived in the USA I would get a single tested 6AQ5 replacement from Jim McShane. Other wise you can do the ebay thing and take your chances, unless you have dealt with a seller already. Another option is ebay and Russian tubes, I bought some Russian 6V6 (6P6S) recently that I really like, they are still quite an economical choice.

The 6AQ5 "family" includes 6V6 and the Russian close equivalent 6P1P (and Chinese 6P1). Unfortunately they all use different bases, 7 pin, 8 pin and 9 pin, and they have different max anode voltages, which allows a little more power to be squeezed out of the 6V6. There is current production 6V6 but the 6AQ5 and 6P1P are all NOS. The Russian 6P1P usually goes for around $2 if you buy a few, and a few dollars for the Russian 6V6. As I said though the chances are that the 6AQ5 you have is fine, I wouldn't even bother buying a spare if the bias voltage is somewhere close to spec for the quiescent current and B+ and screen voltage.