What amplifier for 1940's pickup?

[DavidBJames]

I have a 1940s Portadyne U56 radiogram with a Collaro AC-47 record player (see picture).

The Collaro is mechanically fine - nice steady 78rpm.
I've given up even thinking about restoring the Portadyne U56.

So "Cunning Plan B" -
Install another amplifier at the back of the very large cabinet, bypassing the Portadyne, but preserving power to the turntable. Just use this machine as a 78 record player.

But - what on earth would I use as a replacement amplifier?
What would work with a 1940s magnetic pickup? (see picture)

All advice from "go for it" to "dont be a nutter" gratefully received.

[wd40addict]

Why is the Portadyne unrestorable? Surely you could get its amplifier going even if you didn't bother with the radio side?

[rontech]

LOve the whole unit!

I would test the pickup into any old amp you have to hand or if you have access to a an oscilloscope, have a look at what it is producing.

I think there are number of folk on here with experience of the restoration of old pickups.

I have used Quad 303s for this type of thing. They seem available on line at reasonable prices.

[PaulR]

I think the answer must be "don't be a nutter". The amp in the portadyne must be the best one for the pickup as they were put together by the manufacturer. I doubt that it would sound much better with a hi-fi amp and speaker due to the limitations of the pickup and 78 RPM records in general.

Probably most on here would say restore the existing radio and enjoy it as intended.

[Edward Huggins]

You may not have thought this through. Even if you were to install another valve amplfier (you have to find/build a suitable single channel amp first) there will be the issues of heat dissipation and the need to drill holes in the cabinet to accomodate the additional controls. OK, so if you put a transistoried amp in, you would have to pay very careful attention to the impedence matching of the PU head to the new amp. and ensure that the output impedence would be c.3 ohms. You will also destroy the integrity of the orignal unit which is collectable in its own right. I certainly would not recommend you attempt such a dubious modification.

[Bufo Bill]

David; the guys on this forum got me through fixing my amp and restoring my preamp. If they can get me this far, they should have no trouble helping with your problem. Your system is lovely, do it justice!
Bill.

[Radio Wrangler]

Aye, you've just laid down a challenge.

It's a magnetic pickup, so transistor amplifiers would work fairly easily, but you've already got a nice period amplifier right there... unless some filthy rotten swine has nicked the output bottle(s)

David

[PaulR]

Originally Posted by Radio Wrangler

... unless some filthy rotten swine has nicked the output bottle(s)

David

Even then I doubt they are PX4s !

[AC/HL]

The unit is complete, this is a just change of plan: https://www.vintage-radio.net/forum/...d.php?t=165909

[Edward Huggins]

An Addendum to my earlier Post. In terms of an amplifier restoration on this, which some of us have endorsed, we don't know what experience the OP has? Especially as this Radiogram uses a "live" chassis.

[Herald1360]

Hmmm..... If you don't fancy fixing what's there (I believe it's a live chassis radio job) then anything reasonable, valve and ready to go in the amplifier only line will be quite expensive!

However, a small '40's - '50's AC only woody radio up and running would provide a 3W or so amplifier for the using, maybe even with PU input sockets for a good bit less than just a similar performance straight amplifier.

Some of the less popular small record players might yield up a suitable amplifier too, though one with a two stage amplifier (like the radio) would be better suited than a single stage one used with a high output crystal cartridge. A live chassis type can always be fed from a small isolating transformer.

Otherwise there's plenty of cheap small kit available- mini amplifiers you can run from a 12V dc supply or even the amp from an old micro-hifi system.

[Ed_Dinning]

Hi David, some of these mag pickups had problems with the rubber suspensions (easily fixed) or the coils going open (easily rewound). So it may pay you to check it is actually working first.

Ed

[Radio Wrangler]

I'm not at all a fan of live chassis. If mine, I'd probably save it as a turntable only.

As a kid in the fifties, we had a Colombia turntable with a similar head sitting in a cabinet with a sequential stay that fascinated me. The pickup was connected to a rather nice Murphy console radio.

David

[PJL]

Some cheap modules from China should work.

[Silicon]

I would test the pickup first before going to the expense of modifying the radio.

Do you have any amplifiers that have low level inputs for turntable cartridges, microphones or guitars?

You could connect a screened lead to the original pickup wires and take the signal to an external amplifier.

Some pickups have rubber suspension components that turn hard and brittle.

They need to be replaced. I believe some forum members have moulded new 'rubbers' from neutral cure silicone sealant.

[music-centre]

Just my personal opinion but I cant see what use it would be if you put modern electronics in it, if you like playing 78s its never going to be the best thing to be playing them on due to the limitations of the pickup and probably won't get used much.

I would restore the chassis that is in it and then you get a radio as well as being able to play your records on it and you have an original interesting item.


Steve.

[Heatercathodeshort]

Definitely check the pick up coil for continuity. It will be a lot easier to repair the amplifier than attempt to rewind thousands of turns of wire that is so thin that you can only see it with a white card placed behind it.
The old pick up will require it's damping rubbers replaced. This is a tricky job and often results in the pick up going O/C due to disturbance of the needle armature, coil and magnet.

The original set up will sound nice once you have sorted the amplifier. Adding a modern amp in my opinion is 'nasty'. good luck with it whatever your choice. John.

[crackle]

Its probably easier to fix up the existing radio and amplifier chassis than to fit a new amp in and sort out all the power supply, controls, and other matching problems.
Then you have a genuine functioning item.

Mike

[DavidBJames]

Wow. that generated a lot of interest. Opinion divided between (1) fully restore a very nice radiogram (understandable from this community) and (2) get something working, if only the turntable.
Consensus, though, is check-out the pick-up first. Right - I'll take the signal to an external amplifier and see what I get.
This isn't a priority project. Might be a while before I get back here with results. Thanks all.

[Heatercathodeshort]

Good luck and let us know. John.