UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Australian HMV Rhapsody Radiogram. Replacing Amplifier

lonnyholl · 25th Jul 2022, 2:08 am

Hello Forum
I usually tinker with Industrial Electrics/Electronics, and mostly I have skills to build replace and fault find.

- so audio amplifiers are not my thing however..and looking for some assistance - this unit is for a close family member and has the sentimental value as well... so I need to try and see what can be done to help keep this lovely period piece as more than furniture.

It is an Australian HMV Rhapsody Radiogram from 1969 - it uses a T8-49 Chasssis.

At the moment one channel is weak....the unit uses unobtainable Australian Manufactured Transistors from Fairchild.

I currently have the chassis on the bench, visually I cannot see any damage burning, bloating of caps, or bad connections..looks clean.

The unit comes has an AM Radio and a BSR A10 Turntable with a C1 Cartridge.

If I cannot get the weak channel going by changing its caps...then I will assume one or more of the unobtainable transistors are gone.

Then need a plan B - I am looking to see if its possible and what needs to be considered in replacing the amplifier with some relatively cheap amplifier module....as can be seen on the net - there are certainly lots to choose from these days.

I have a few questions with that in mind.

I do know the BSR C1 Cartridge outputs 43mV

I am not 100% sure but measuring radio audio signal output appears to be from 2-10 mV

Thats about the only specs I know -
My questions are - what would I need to do and consider in matching a replacement amplifier module to the existing inputs I have.

Two things Im not sure about is - would a replacement module be able to amplify existing signals directly.... considering the low outputs from both the BSR and Radio...(would I need a Preamplifier)...and what about matching impedance to the amplifier - what should be considered/required to make it work?

Lastly - Ideally I would like to retain the existing Volume, Tone, Balance Control Pot's....is this at all possible ?.....or do I need to find a Preamp Module which has existingVol/Tone/Bal Pots and replace existing Audio controls.

I thought members may have had these challenges before with using new amplifier modules due to unobtainable Components and hope to hear from Peoples experiences and thoughts.

Schematic as shown.

Many Thanks

25th Jul 2022, 2:08 am	#1
lonnyholl Triode Join Date: Jul 2022 Location: Brisbane, Queensland, Australia. Posts: 42	Australian HMV Rhapsody Radiogram. Replacing Amplifier - Questions!? Hello Forum I usually tinker with Industrial Electrics/Electronics, and mostly I have skills to build replace and fault find. - so audio amplifiers are not my thing however..and looking for some assistance - this unit is for a close family member and has the sentimental value as well... so I need to try and see what can be done to help keep this lovely period piece as more than furniture. It is an Australian HMV Rhapsody Radiogram from 1969 - it uses a T8-49 Chasssis. At the moment one channel is weak....the unit uses unobtainable Australian Manufactured Transistors from Fairchild. I currently have the chassis on the bench, visually I cannot see any damage burning, bloating of caps, or bad connections..looks clean. The unit comes has an AM Radio and a BSR A10 Turntable with a C1 Cartridge. If I cannot get the weak channel going by changing its caps...then I will assume one or more of the unobtainable transistors are gone. Then need a plan B - I am looking to see if its possible and what needs to be considered in replacing the amplifier with some relatively cheap amplifier module....as can be seen on the net - there are certainly lots to choose from these days. I have a few questions with that in mind. I do know the BSR C1 Cartridge outputs 43mV I am not 100% sure but measuring radio audio signal output appears to be from 2-10 mV Thats about the only specs I know - My questions are - what would I need to do and consider in matching a replacement amplifier module to the existing inputs I have. Two things Im not sure about is - would a replacement module be able to amplify existing signals directly.... considering the low outputs from both the BSR and Radio...(would I need a Preamplifier)...and what about matching impedance to the amplifier - what should be considered/required to make it work? Lastly - Ideally I would like to retain the existing Volume, Tone, Balance Control Pot's....is this at all possible ?.....or do I need to find a Preamp Module which has existingVol/Tone/Bal Pots and replace existing Audio controls. I thought members may have had these challenges before with using new amplifier modules due to unobtainable Components and hope to hear from Peoples experiences and thoughts. Schematic as shown. Many Thanks Attached Thumbnails