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How can I use a phonograph ready tube radio as guitar amp? Answered

Has phono terminal board with 3 screws. Instructions say to remove link between terms 1&2, connect green from phono to 1,  yellow to 2 & shield ext to 3, tape off red & blue. 

Radio is fully functional. 

Thank in advance for your help. 

Sorry if I've added multiples of images, I can't seem to load them. 

13 Replies

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Josehf Murchison (author)2014-12-31

Unfortunately I can't see your picks.

Most have a selector switch for radio or phonograph, however I think yours has a solid link you disconnect.

Remove the link and connect your guitar to the amp input and ground.

1 or 2 is the input and 3 should be ground would be my guess.

You may have to try it on 1 then try it on 2 to find the input.

Then to get the radio back return the links to the way you found them.

Joe

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user

Thanks Joe,

Maybe the first order of business is figuring out what the problem is with me and posting pictures.

You are correct, there is no phono selector switch.

I tried 1 & 2 as input, assuming ground on the guitar cable is the outside - if that matters. No result.

That said. The tuning belt has broken so I can't now be certain the radio is working. Of course it would break when receiving NO radio signal.

I'll have to pull the chassis.

Wiring diagram says 'close link for radio' so that answers one of my question. Duh!

Thanks for your help.

Andy

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user

It’s not your posting of picks the files are converted when you upload them loosing detail, then to make matters worse I am legally blind, so blowing them up doesn’t help.

There is one other possibility the radio output is made to match the phonograph pickup output and your guitar output is completely different.

Pickups work two ways.

1 create a current

2 impede a current

Your guitar pickup may create a current and the radio or the phonograph pickup may impede a current.

Think of pickups as a sound activated variable resistor or a sound activated generator. If you need one the other won’t work.

Is the tuning belt a belt or a string?

If it is a belt you will probably need to make one.

If it is a string you need a linen string not cotton, hemp, or plastic, nylon or silk might work.

Joe

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user

Thanks Joe,

If I remember correctly it was a belt. As a temporary fix an elastic band did the job. I forget why I did that, I was checking something. That somehow lasted about ten years.

On youtube some one posted his refurbish of the same model. Not step by step, more or less just showing the work already done. He purchased a belt on line. Possibly leather?

It would me great to know the correct diameter rather than fiddling around. With luck it would match up with an o-ring size. I know sewing machines use them.

Andy

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iceng (author)2014-12-30

So do that, with the Tube unit unplugged and the volume at the lowest CCW setting.

Switch to phono and plug the unit in and turn it on.

Then strum your guitar.

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Tenor nidan (author)iceng2014-12-30

Thanks

What does removing the link between terminals do? Will the radio still function without the guitar plugged in (completing a circuit?)?

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iceng (author)Tenor nidan2014-12-30

The link is the signal ground strap for the high gain magnetic preamp.

I don't know. There should be some kind of switch, maybe a rotary knob that stops the radio and links the phono.

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iceng (author)iceng2014-12-30

Is there a phono plug receptacle in the unit ?

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Tenor nidan (author)iceng2014-12-30

No. Just the three screws

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iceng (author)Tenor nidan2014-12-31

Reading fig-4 of your pages it appears opening that 2-3 link disables the radio and enables the phono signal acceptance on the 1-3 shield signal pins.

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Tenor nidan (author)iceng2014-12-31

Thanks iceng.

Could it be that the signal from a guitar is just too weak?

.

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iceng (author)Tenor nidan2014-12-31

Probably because there is no pre-amp, and the text does mention adding an additional gain unit.

A guitar is the same level of output as a magnetic phonograph cartridge.

Both really need that pre-amp.

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Tenor nidan (author)2014-12-31

okay, looks like three pic loaded

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