Sylvania Console amp

[Kyri]

Hi!
I recently acquired this amp. I have started using it and it sounds great.
It is a US unit so I have to step down the voltage.
I have limited experience with repairing or modifying tube amps, and have been reading around to get an understanding and thought this place would help accelerate my learning.

I have added some connectors for speakers, and a 2A fuse to the live/line input but have some questions.
1. Does anyone know anything about these amps? Or even have a schematic for it?
2. Is he 128V I have measured coming in, too much? Should I use a variable transformer to lower it to 120v compared to the auto transformer I am currently using. Is our 50Hz plus slightly higher voltage, ok. The transformer is warm (not hot) in use.
3. I read about electrolyic caps drying up over time. This amp works really well, is there a test I can do to see if the existing power caps are ok, or should I just add some new ones and bypass the old. I am sure I could figure out how to do that. This 80/40/20 cap does not get warm during use, and "looks" ok but I haven't done any tests on it.
4. I was informed and read about some bypass caps leaking / passing DC leading to trouble - but these caps are all ceramic, so should I leave them?
5. Resistors, what about them?

I am not experienced in measuring voltages whilst powered up but could do it if needed, (measuring input voltage for ex.) I have a healthy safety awareness and know that high dc voltages are dangerous.

This amp sounds so good, that I really want to use it and enjoy it. I don't want to change things just for the sake of it so have limited my changes to inline fuse (on live/line), earthed lead (made no difference to hum).

Any advice or comment would be really appreciated. Some pictures for info.
Thanks!
Kyri

[Techman]

Is it really made by Sylvania?

The valves are Sylvania - not sure about the amp itself, it looks almost homemade with what looks like a chassis made of galvanised steel bent on a metal bending machine by someone in their lunch break at work, but I could be completely wrong.

It looks very good, other than those not very big output transformers stuck on the back. I don't think you need to worry about anything in that amp. As you've already found, the smoothing can is running cool and those are definitely ceramic coupling capacitors, so I would leave it alone and enjoy it.

As for a circuit diagram - you won't need one for something that simple. Just download and print off the data for the valves and follow basic amplifier principles to work out what's what...should you ever need to.

Check the valve heater voltages as a guide to correct voltage from the step down transformer.

Edit to say - it looks from the stuck on labels like it has been made by perhaps a small company somewhere, so who knows, but I quite like it...other than the 'look' of those transformers on the back, but maybe it was found that there was nowhere else to fit them without a hum problem.

[Lloyd 1985]

Maybe it was originally part of a gram?

Sounds like it’s working fine though, and those ceramic caps will most probably be ok, they last much better than wax paper caps. The large electrolytic cap would have let you know by now if it wasn’t happy, either with loud mains hum on the audio, or the can heating up.

As for getting a circuit diagram for it, if it was part of a radiogram then looking up the model number of that would probably help.

Regards
Lloyd

[Robert Gribnau]

What is written on the front panel, left of the inputs? And is there something visible/readable on the (faded?) marking on the right side of the front panel?

[Edward Huggins]

Definately leave it well alone! Those OP transformers do look rather small, but may be perfectly adequate for what looks like a SE output stage. What's the valve line up?

[Kyri]

Originally Posted by Lloyd 1985

Maybe it was originally part of a gram?

Sounds like it’s working fine though, and those ceramic caps will most probably be ok, they last much better than wax paper caps. The large electrolytic cap would have let you know by now if it wasn’t happy, either with loud mains hum on the audio, or the can heating up.

As for getting a circuit diagram for it, if it was part of a radiogram then looking up the model number of that would probably help.

Regards
Lloyd

Lloyd, there is a reference I found when searching which is 45C36D, and I am sure I saved the pictures I found as well, need to dig them out. It was for an amp that looked identical.

Originally Posted by Techman

Is it really made by Sylvania?

The valves are Sylvania - not sure about the amp itself, it looks almost homemade with what looks like a chassis made of galvanised steel bent on a metal bending machine by someone in their lunch break at work, but I could be completely wrong.

It looks very good, other than those not very big output transformers stuck on the back. I don't think you need to worry about anything in that amp. As you've already found, the smoothing can is running cool and those are definitely ceramic coupling capacitors, so I would leave it alone and enjoy it.

As for a circuit diagram - you won't need one for something that simple. Just download and print off the data for the valves and follow basic amplifier principles to work out what's what...should you ever need to.

Check the valve heater voltages as a guide to correct voltage from the step down transformer.

Edit to say - it looks from the stuck on labels like it has been made by perhaps a small company somewhere, so who knows, but I quite like it...other than the 'look' of those transformers on the back, but maybe it was found that there was nowhere else to fit them without a hum problem.

Thanks for the detailed reply - As far as I gathered from the seller it came from a Sylvania branded console. The model number I found a reference to (45C36D) and as I mentioned to Lloyd I will try to find the thread or pictures it referred to. I saved the pictures somewhere but not the link.

Originally Posted by Robert Gribnau

What is written on the front panel, left of the inputs? And is there something visible/readable on the (faded?) marking on the right side of the front panel?

It says "Stereo Tape" and there is another set of inputs which were leads which I have insulated and put back inside the amp with yellow heat shrink on the ends. I was told they were for the record player, there was also a 3 lead output with a plug on the end, which apparently switched on the amp when the record player was used. I removed that but could add it back if needed.

Here is a picture of the front panel.

Originally Posted by Edward Huggins

Definately leave it well alone! Those OP transformers do look rather small, but may be perfectly adequate for what looks like a SE output stage. What's the valve line up?

Hello Edward, the output transformers do look small, but seem to do the job well. I paired up the amp to a set of mid-80's monitor audio 8 ohm speakers which really sound good with it, and more than loud enough for my purposes. I was told that the amp was for a 3ohm output but have no way to verify that and since it works so well I might leave it as it is. I understand that putting higher impedance speakers may lower the output but is not damaging to the amp, compared to the other way round, but I do need to study and learn more on mismatches.

The only real issue I have in using these speakers is that the rest of the family keep telling me that it doesn't sound the same in the kitchen anymore and when can I put the old speakers back!!!!

As for valve line up, 5Y3GT, 12AX7 and 6BQ5. I am more familiar with the british equivalents and have mostly mullard ECC83 and EL84's in my guitar amplifiers. These "tubes" look and sound very nice, appear to be well matched and I don't really want to abuse them hence my questions and this thread.

[Techman]

Originally Posted by Kyri

As far as I gathered from the seller it came from a Sylvania branded console.

Yes, it was definitely originally fitted on its side, although I did wonder whether the amplifier had been built by someone to fit an already available front panel, but it now seems that it definitely came from some sort of radiogram - console is an Americanism like calling valves tubes - in the UK a 'tube' is the large glass thing that displays the picture on an old school TV set. I would try and drop the 'Americanisms', the only one I really like is "red plating", which I think is very descriptive and describes the red glowing of the anode of a valve when it passes too much current, which would possibly be the case in your amplifier if those ceramic coupling capacitors were actually old leaky paper types instead of those quality types that you have.

You mentioned a 'hum' in your first post. If it varies with volume control then it's probably something to do with lack of screening/earthing somewhere in the input, but if it's there all the time regardless of the volume control setting, then it needs further investigation and may be smoothing or even pickup in those transformers.

[Kyri]

Originally Posted by Techman

You mentioned a 'hum' in your first post. If it varies with volume control then it's probably something to do with lack of screening/earthing somewhere in the input, but if it's there all the time regardless of the volume control setting, then it needs further investigation and may be smoothing or even pickup in those transformers.

This is very interesting to me. The hum is a low level 50hz one which is there as soon as the amp is plugged in and even before it warms up. It is really not a problem from a usage point of view, and nothing I have done has made it any worse. Before I replaced the non polarised mains lead I tried it both ways round and could not tell a difference one way or another. Adding the earth made no difference either.
I tried a different input lead as the first one I had made up with a jack plug and some phono plugs. The one I purchased should be better screened. Again, no difference.

I am interested to know about the smoothing, and why would that affect the hum. Is the fact that this is designed for 60hz a factor here?

[PaulR]

Does the hum come from the amp itself or through the speakers? If just from the amp then it is just a mechanical hum coming from the mains transformer. As others have said it is probably best simply to enjoy the amp but if you need it there is a Sams manual for the 45c36 series under their item number 175567. It is $15 so might not be worth buying just for the amp. Presumably it contains details for the rest of the radiogram. https://www.samswebsite.com/en/photo...ndex/id/175567

Regarding the term "console" we had a freestanding radio and a TV set and my mother referred to them bot as "consoles"

[Techman]

I agree that it sounds like a mechanical hum from the mains transformer.

Measure the heater voltage of one of the output valves (remember what I said about looking up and downloading the valve data), I would expect around 6.3 volts AC...plus or minus a little, this will tell you whether you're over or under running the amplifier with that step down transformer. Be very careful with your meter probes that they don't slip while your taking readings or there may be a flash and a bang. If you're at all unsure about what to do, then ask for advice from members.

[Kyri]

Originally Posted by Techman

I agree that it sounds like a mechanical hum from the mains transformer.

Measure the heater voltage of one of the output valves (remember what I said about looking up and downloading the valve data), I would expect around 6.3 volts AC...plus or minus a little, this will tell you whether you're over or under running the amplifier with that step down transformer. Be very careful with your meter probes that they don't slip while your taking readings or there may be a flash and a bang. If you're at all unsure about what to do, then ask for advice from members.

Thankyou, I did get the data to find pin 4 and 5 for the heater - is it better to do this with all the valves in, or is there any advantage to taking the valves out. I suppose the voltage might be higher without due to no load so might hide what I am looking for?

[Kyri]

Ok, I decided to power up, valves and speakers connected, but no input.

The output valve heaters link to the dark green wires on the transformer so I clipped onto one of them where it joins to the pink wire on the post, and measured with the probe on the other post where the other green wire joins. A little easier than messing round the valve bases. (the pink wires go from the posts to the pins 4&5 on the EL84's).

The reading was 6.8V across the heaters, and the mains input measured 127.7V.

Regarding the hum I paid attention to where the noise was coming from and whilst there is a faint hum from the speakers the majority is coming from the auto transformer as soon as it is plugged in! The transformer on the amp is quiet - or at least relatively as with the noise from the other one I can't hear it.

[Techman]

Well done with that test. You did it the best way by taking readings at the transformer with all valves in place. Always have a speaker connected with a valve amplifier, as running one off load can cause damage, so you did the right thing there. 6.8 volts is a little high in my opinion, I would rather it be no more than 6.5 volts, although a lot of valve gear from the continent set to run on 220 volts tends to have high readings around that voltage, and there's the clue. Your auto transformer is a bit of a general purpose one intended to run on 220-240 volts and a lot of the UK mains tends to run on the high side (I've just measured mine at 241 volts), also its voltage output will be when fully loaded to its rated level, which your amplifier won't be doing. You really need something more specialised so that you can fine adjust the primary input tapping for a particular local mains voltage.

I don't know whether to tell you to worry about that over voltage or not. It'll mean that the amplifier is working at top performance, but with possible shortened valve life. Measuring the HT voltage won't tell you a lot, as it can be variable with individual design, but you could check DC voltages particularly around the two output valves to check that they're not above the maximum specified in the data. One definite check that you should make is at the first smoothing capacitor, which will be the reservoir immediately after the rectifier to make sure that it doesn't exceed the 'working voltage' printed on the side of the can, if it does then you'll definitely have to do something regarding the step down transformer. Remember, meter set on the highest DC voltage range for these tests, probably 600 volts and be particularly careful with the probes - negative to chassis.

[usradcoll1]

Originally Posted by Techman

Is it really made by Sylvania?

The valves are Sylvania - not sure about the amp itself, it looks almost homemade with what looks like a chassis made of galvanised steel bent on a metal bending machine by someone in their lunch break at work, but I could be completely wrong.

It looks very good, other than those not very big output transformers stuck on the back. I don't think you need to worry about anything in that amp. As you've already found, the smoothing can is running cool and those are definitely ceramic coupling capacitors, so I would leave it alone and enjoy it.

As for a circuit diagram - you won't need one for something that simple. Just download and print off the data for the valves and follow basic amplifier principles to work out what's what...should you ever need to.

Check the valve heater voltages as a guide to correct voltage from the step down transformer.

Edit to say - it looks from the stuck on labels like it has been made by perhaps a small company somewhere, so who knows, but I quite like it...other than the 'look' of those transformers on the back, but maybe it was found that there was nowhere else to fit them without a hum problem.

Being more familiar with US made products, Sylvania did have some of their product lines made by other smaller manufacturers. Zenith, Philco and the other large firms did the same thing.
That amp looks rather well constructed, a decent sized mains transformer, higher quality components, fancy tone compensating volume control, ETC.
In spite of the small output transformers, it probably sounds rather good.
Dave, USradcoll1

[PaulR]

Yes it is a Sylvania product. There is a Sams for it https://www.samswebsite.com/en/photo...ndex/id/175567

[snowman_al]

The little emblem posted by the OP shows the Sylvania stylised 'S' or lightening flash in a shield.

[Techman]

But what do we reckon about the over-voltage, folks?

I actually think that it would probably be OK so long as the valve parameters are not exceeded (by much) and the main electrolytic smoothing capacitors are not being over-voltaged. I think if these are within limits, so long as the amplifier isn't given long continuous use for many hours a day, then the valves will survive - I seem to remember finding something like 7.2 volts on a 6.3 volt heater supply on an Italian amplifier with a transformer probably wound for 220 volts - the output valve had a short but brilliant life!

[snowman_al]

If it were mine, I would get the AC input voltage down to 115-120volts regardless. We do not know if the mains transformer was designed to run on 50Hz though it does look comparatively 'chunky', so anything to keep the heat down would be a good idea?
That would also take some stress off the remaining components.

[Kyri]

Originally Posted by Techman

I don't know whether to tell you to worry about that over voltage or not. It'll mean that the amplifier is working at top performance, but with possible shortened valve life.

I thought about this and guess what arrived today. I chose not to buy new and am very pleased with the result.

I set up the variable transformer with bulb and dialled it to 117V (or close) and then re-did the heater checks. Exactly 6.3V!

You were right about the step down transformer, the other thing to note is that the variable transformer dial is quite sensitive so I will have to find a way to fix it. I decided to put a female US plug on the output to the variable transformer to prevent the amp being plugged directly into the mains should I have put a UK plug on it.

Regarding the setup, I have been using a 1A fuse and it blew, when I tried to power up again after doing the measurements. I swapped it with a 2A fuse and it powered up. A couple of questions:
1. How do I know what fuse to use , 1A or 2A, and what type as these are conventional ones but how do I know which fuse is right. I had read somewhere that a 2A fuse would be ok. However I also read that there are different types of fuses. Which is most appropriate here (assuming no underlying problems)
2. If the fuse fails on switch on is this an indication that the smoothing caps aren't doing what they should?

[Kyri]

In spite of the small output transformers, it probably sounds rather good.
Dave, USradcoll1

Dave, thanks for this, you are right, it sounds great! All the help I am getting here, will hopefully keep it that way