1957.. convert a old receiver with field coil speakers into a guitar amp?

I have a 1957 Phillips Receiver.. there's no option for restoring the record deck and the we will soon loose analogue radio.. (bluetooth streaming I know about)

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Here's it after my restoration.. replacing the leaking caps and installing a shunt for the modern high wall voltage.

However it doesn't get used.. and I was thinking that an option could be to plunder its components and build a 1957 styled/voiced guitar amp which is likely to get more use. I've got a load of ply left.

I'm just trying to consider if this is worth it..
 
That kind of midrange consumer receivers often had a weak amplifier and low quality speakers. Your Philips appears to be a safe design with power transformer so you can connect audio sources to the line level input. I would try at first to evaluate the quality of the output transformer and speakers by connecting the guitar to a pedal/effect and use the output to feed the signal to the Philips. If the cabinet still looks good, the receiver may have some collector value and you may just remove the tubes for your project. EZ80, EL84, EABC80 and ECC85 are fine for audio use.
 
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In my youth I acquired a bunch of large (12 and 15 inch) field coil speakers from the dumpster at Victor Pianos and Organs in Miami (they still exist) and proceeded to make a solid state guitar amp based on a LiL Tiger (20 watts mono) mated with a DIY germanium preamp built with transistors robbed from old radios. The field coil was powered with rectified and filtered line voltage through a big resistor. It sounded great...... for a while.

The amp had a low frequency response that went too low for the speakers being used. If one would get heavy handed on the guitar strings, the voice coil would bottom out creating a loud pop. Do this a few times and the old phenolic voice coil former would disintegrate rendering the speaker useless. Eventually I killed them all. This may not happen with a tube amp and an OPT, but if you hear the pop, change some coupling cap values.

I replaced the field coil speaker with a PM guitar speaker from Olson Electronics which was a rebranded Utah. (remember them?) That amp lived on until I left home and gave it away.
 
I'm guessing that filter would be required to roll off the bass giving it a period sound. This would be less rock/metal.

I know the real speakers of the time, Jensens and the like, would be more suited but the same oval speakers were present in things like the Gretsch which is what got me thinking.