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Old 13th June 2012, 01:55 PM   #1
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Default Sylvania 45C14M advice

I have built a few guitar tube amps from kits and wanted to get a basic tube Stereo going. so I just got this Sylvania 45C14M on Ebay for $50 to tinker with. I won't have it for a week or so but I would like to start gathering information as soon as possible.

according to the seller, it works as is and the tubes test strong so I shouldn't have to do much
( but we will see)

Click the image to open in full size.

The thing I will need help with is adding a bypass for the Phono Input/EQ for a Mp3 line in. I was thinking about using a rotary switch so that I could still use the phono input for a turntable. would this even be possible? If not I will just use LP's only, no big deal. I am trying to find Schematics and diagrams that I don't have to pay for but so far i have had no luck.

if anyone has some experience with this amplifier I would appreciate any advice you can provide.
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Old 13th June 2012, 08:57 PM   #2
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I got a copy of the PhotoFact Manual, for SYLVANIA 45C13 / 45C14 (#508) for $6 so I will upload the schematic page when I get it. maybe someone can guide me a bit through the process. I can read schematics as far as whats there and where its going, but as to why and what it does I am a little lost still.
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Old 18th June 2012, 02:22 PM   #3
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I have the schematic now

http://img215.imageshack.us/img215/5774/45c13page2image0001web.jpg
http://img26.imageshack.us/img26/6083/45c13page4image0001web.jpg

I have a few questions.
can anyone tell me if this has the RIAA cruve circuit in it?
I know what the rumble filter does and i think K3+K6 is just the EQ circuit between preamp and power amp. but what is the K1+K4 tone comp ? is that tone compensator as in the RIAA curve circuit ?

also based on the schematic would it be safe to run an mp3 player into the inputs,
or would that be to much input gain?

and last one, would the rumble filter affect MP3 playback sound much?

If I can just use it as is without the circuit altering the input signal much I will just leave it alone

again I would appreciate any advice.
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Old 18th June 2012, 06:31 PM   #4
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Very interesting! A sum and difference amplifier - I've never seen one before, and I thought I'd seen everything. The two inputs are not left and right, but rather vertical and horizontal outputs from the phono cartridge.

To use this with conventional left and right stereo inputs will require either changes to the amplifier or a sum and difference matrix ahead of it. Personally, I'd be tempted to change to two (identical) conventional output transformers.

All good fortune,
Chris
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Old 18th June 2012, 06:31 PM   #5
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The amplifier has a loudness-compensating volume control (K1) and a fixed equalization circuit (K2).
Before changing anything in the amplifier, I suggest that you connect your MP3 player and listen for a few days.
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Old 18th June 2012, 06:47 PM   #6
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Quote:
Originally Posted by Chris Hornbeck View Post
Very interesting! A sum and difference amplifier - I've never seen one before, and I thought I'd seen everything. The two inputs are not left and right, but rather vertical and horizontal outputs from the phono cartridge.

To use this with conventional left and right stereo inputs will require either changes to the amplifier or a sum and difference matrix ahead of it. Personally, I'd be tempted to change to two (identical) conventional output transformers.

All good fortune,
Chris
If you don't mind can you explain this further? I have never heard of this before,
I thought it was just 2 parallel mono amps in there.

Quote:
Originally Posted by Frank Berry View Post
The amplifier has a loudness-compensating volume control (K1) and a fixed equalization circuit (K2).
Before changing anything in the amplifier, I suggest that you connect your MP3 player and listen for a few days.
so far I have had it hooked up to a set of cheap 8 ohm bookshelf speakers here at work and it sounded fine. I did have the mp3 player at low volume though. also there is no hum at all when idle, I expected some ac hum.

also if you dont mind can you explain loudness-compensating volume control and a fixed equalization circuit ? I would appreciate it. like i said this is new territory for me
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Old 18th June 2012, 07:12 PM   #7
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Quote:
Originally Posted by somebizarredude View Post
If you don't mind can you explain this further? I have never heard of this before,
I thought it was just 2 parallel mono amps in there.
That's the way every other amp you'll ever see is made, but this one's unique. Look at the output transformers and you'll see why. This amp is made for the single purpose of use with a special (unique except for Decca, I think) stereo phono cartridge with sum (horizontal) and difference (vertical) outputs. At the amp's outputs, they're matrixed into left and right channels. I'm surprised that there's much stereo difference to the outputs. Are they in phase?

All good fortune,
Chris
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Old 18th June 2012, 07:33 PM   #8
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Quote:
Originally Posted by Chris Hornbeck View Post
That's the way every other amp you'll ever see is made, but this one's unique. Look at the output transformers and you'll see why. This amp is made for the single purpose of use with a special (unique except for Decca, I think) stereo phono cartridge with sum (horizontal) and difference (vertical) outputs. At the amp's outputs, they're matrixed into left and right channels. I'm surprised that there's much stereo difference to the outputs. Are they in phase?

All good fortune,
Chris
I wasn't able to do much testing here at work, I only had a 30 minute lunch break. but when I get home I will test it more. It didn't sound like L&R are out of sync, if they are its so little i didn't notice. I will play some tracks with L/R panning later to see what happens. This reveals how little i know about Phonographs

also on another note based on the schematic what kind of head would you recommend I use in a phonograph that will work well with this circuit?
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Old 18th June 2012, 07:39 PM   #9
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These "matrix" stereo amps had a brief run, didn't last long - will only work with out-of-phase inputs, so aren't usable with a tape input for instance... Maybe they were planning to eliminate some parts in the FM multiplex decoder! But I don't think they even lasted until FM stereo started.

Here's an article about the principle: http://www.audiofaidate.org/it/artic...rst_matrix.pdf

I would replace the output transformers and use it as a stereo single-ended amplifier.
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Old 18th June 2012, 07:52 PM   #10
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Originally Posted by Tom Bavis View Post
These "matrix" stereo amps had a brief run, didn't last long - will only work with out-of-phase inputs, so aren't usable with a tape input for instance... Maybe they were planning to eliminate some parts in the FM multiplex decoder! But I don't think they even lasted until FM stereo started.

Here's an article about the principle: http://www.audiofaidate.org/it/artic...rst_matrix.pdf

I would replace the output transformers and use it as a stereo single-ended amplifier.
Thats what I would like to use it for, but i wouldn't know where to start as far as what transformers I should use. I would need a guiding hand for that and this being so unusual is it valuable and should I just leave it alone? it seems to work just fine for what it is
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