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Post by mark52404 on Jan 27, 2021 18:55:42 GMT 12
Hi all I am new to this forum and the world of vintage radiograms. I have recently purchased a functioning Bell Truetone 1957 which looks to have a replacement turntable fiitted (BSR McDonald 610). The rest looks original, externally. My queries is: - I think I have a volume issue when the turntable is selected. The volume is great (loud and clear) when the radio is selected, however very quiet when the turntable is selected. Any ideas on what the issue maybe? - Are there any reputable repairs/restorers for these in the Wellington region? - Any other info on this radiogram would be greatly appreciated. Cheers, Mark    |
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Post by Richard on Jan 28, 2021 7:24:57 GMT 12
Most likely answer is, that the newer turntable has a ceramic cartridge, when the original turntable would have had a crystal cartridge. Crystal cartridges had a higher audio output level than Ceramic Cartridges. This means you would need to add a pre-amp to get the level up to feed the original valve amp.
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Steve
Society Members
vintageradio.co.nz
Posts: 727
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Post by Steve on Feb 6, 2021 10:29:54 GMT 12
If it is a cartridge issue and you want to make something period specific to resolve it, Radio Ltd made separate pre-amplifiers for their radiograms in the mid-50's - I can't help thinking I've seen one of the schematics with the preamp circuit included but I can't find it for the life of me - although there is a note from a serviceman on the last page of this one this one showing a magnetic preamp circuit probably reverse engineered from one. They tended to use an EF22 in their preamps. nzvrshome.files.wordpress.com/2018/12/RL-RCE-Baby-GrandSymphony-7V-Bandspread-AC-1955.pdfHere is one in a model RCC  Philips also had preamp circuits on some models - The 1957 Carnegie Hall radiogram came in 3 'MK's - the MK2 had an EF86-based valve preamp for magnetic cartridges (MK1 had a ceramic cart so no preamp needed, and the MK3 had a fancy new transistor preamp) nzvrshome.files.wordpress.com/2018/12/Philips-FZ967A-968A-977A-978A-987A-988A-Carnegie-Hall.pdf - note the MK2 and MK3 circuits are swapped (mis-labeled) in this service info. Alternatively I have read somewhere that the cheap little guitar pickup amps / eq's you can get on Ali Express do a reasonable job - the model I saw recommended was EQ7545 I think... they're cheap as chips at around $15 delivered (actually I spent more than this on fish and chips the other night, so they might actually be cheaper than chips!). I believe they use a 9V battery though, so you might need something like an old wall-wart power supply if you wanted it to stand alone and not run from batteries. If you ever have it apart, I'd love to get some photos to detail the model on vintageradio.co.nz Cheers, Steve |
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Post by Peter Walsham on Mar 18, 2021 21:04:03 GMT 12
I suspect that the BSR turntable has a magnetic cartridge fitted to it, as a ceramic cartridge was reasonably capable of driving a two stage audio amplifier. We used to fit ceramic cartridges to radiograms in preference to crystal, as they had a more even frequency response, and sounded way better. A solid state magnetic pre-amp will boost the output of the magnetic cartridge and provide equalisation required as well.
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