help with a Phillips tube radio

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noiseuoh
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Post by noiseuoh »

hello everyone,
i have a phillips Novasonic B5SF62A tube radio that i have been slowly restoring (it is working ok but there are some problems with a ground loop/whine on the high end). it has two speakers, one for the high end and one for the low end/mids. the high end speaker has an output from the primary side of the transformer and the low end/mids speaker on the secondary side like a normal tube amp would. you can see it on the schematic. the treble speaker on the primary side is very weird to me and makes me believe the speaker is rated for several hundred ohms.
the main problem i have is that i would like to bypass both speakers and use an external speaker. right now i am using the phono input jack for a guitar input. when i disconnect both speakers and hook up an external one i lose a lot of output and it basically becomes unusable. can anyone explain why? im pretty sure the "main" speaker (low/mids) is rated for 8ohms.
if i run the amp normally with its built in speakers it works fine (except for the whine/ground loop on the treble which i am trying to sort out with cap replacements).
does anyone have any ideas about bypassing the internal speakers in a way that would make it work better? should i just ditch the treble speaker altogether? will that affect the functioning of the amp if there is no connection on the primary side? any help is greatly appreciated. thanks
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noiseuoh
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Post by noiseuoh »

just went through the parts list.
the treble speaker is 800ohms and the bass speaker is 5ohms.

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jonsnell electronic
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Post by jonsnell electronic »

noiseuoh wrote:just went through the parts list.
the treble speaker is 800ohms and the bass speaker is 5ohms.
The treble speaker is high impedance to cope with the primary side; it is also isolated with capacitors, to block the DC.
If it squawks when in use, maybe the treble speaker is faulty?
It will not harm the amplifier to run without it.

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noiseuoh
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Post by noiseuoh »

thanks for the input. Yea, thats what i understood also about the high impedance. turns out i disconnected the treble speaker, and the bass speaker and then used the speaker output (rated at 6ohms so shouldve been fine). and then fried a couple of resistors off of the power supply. they were connected from the power transformer secondary and then to the treble speaker. i will try to turn it on tomorrow with those removed. it seems like they are only connected to the treble speaker anyway. hopefully i didnt destroy anything else (ie power transformer).
i guess my main question would be, how would i wire/rearrange components to still get the high end through the main speaker out?

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