Hi all!

OK, so this is my first post here, and me starting down the road of rebuilding a tube amp...

Basically, I picked up a partially-restored teeco-1220 amp, and am planning on using it. The guy I picked it up from had it running with a rather strange arrangement--AC/DC transformer to inverter to feed it 110v, 60 Hz power supply. This caused a certain amount of feedthrough from the inverter, in that there was (apperantly) a constant-volume hum present.

Now, I cannot be bothered with such a strange arrangement, and would prefer to simply make the primary transformer work "nativley" with the power supply I've got here, that being 240v, 50Hz. Thus, it seems to me, I should just be able to swap out the input transformer for something more appopriate, right?

Problem is, though, I cannot figure out what this primary actually is. All that is stamped on it is "PT-156 606028".

Any information about what is supposed to be coming out of this transformer would be greatly appreciated, as it would same me *a lot* of lab work figuring it out...

Also, while I'm here, is my idea for simply replacing the primary transformer in this manner even a valid idea? That is, once this item is taken care of, will it matter to the rest of the systm that the imput power will be at 50 Hz instead of 60 Hz? If so, why?

Thanks in advance!

:Hi all!
:
:OK, so this is my first post here, and me starting down the road of rebuilding a tube amp...
:
:Basically, I picked up a partially-restored teeco-1220 amp, and am planning on using it. The guy I picked it up from had it running with a rather strange arrangement--AC/DC transformer to inverter to feed it 110v, 60 Hz power supply. This caused a certain amount of feedthrough from the inverter, in that there was (apperantly) a constant-volume hum present.
:
:Now, I cannot be bothered with such a strange arrangement, and would prefer to simply make the primary transformer work "nativley" with the power supply I've got here, that being 240v, 50Hz. Thus, it seems to me, I should just be able to swap out the input transformer for something more appopriate, right?
:
:Problem is, though, I cannot figure out what this primary actually is. All that is stamped on it is "PT-156 606028".
:
:Any information about what is supposed to be coming out of this transformer would be greatly appreciated, as it would same me *a lot* of lab work figuring it out...
:
:Also, while I'm here, is my idea for simply replacing the primary transformer in this manner even a valid idea? That is, once this item is taken care of, will it matter to the rest of the systm that the imput power will be at 50 Hz instead of 60 Hz? If so, why?
:
:Thanks in advance!

Waldorf,

You may try a stepdown transformer 220V/110V and run the amp for a few minutes, say 30 minutes, and see if the power transformer gets hot. I am not sure the difference between 50HZ and 60HZ would make a big difference in operation. Others on this forum may have more ideas though.

Radiodoc

Waldorf, as long as you get the correct secondary voltages, the set is never going to "see" the primary voltage or frequency. Unless you have direct heater/ cathodes the frequency never gets into the circuits.PL

: Waldorf, as long as you get the correct secondary voltages, the set is never going to "see" the primary voltage or frequency. Unless you have direct heater/ cathodes the frequency never gets into the circuits.PL

Planigan,

I may be all wet on this, but I gather his amp has a transformer that operates on 110 VAC 60HZ. The power in his area is 220 VAC 50HZ. This is the part I may be all wet on. It seems someone has installed or connected a converter or inverter to convert from 220 VAC 50HZ to 110 VAC 60HZ.

Radiodoc

First, you want to be sure that the amplifier itself is performing properly. If there is any way you can obtain a 220 volt Variac or a step down transformer, operate the amplifier from this. IF you have hum, then the set probably needs its electrolytics replaced, and possibly other condensers (for optimum performance.....leaky condensers are a no-no if you want perfect performance). If the set does not hum from the transformer or Variac, then the problem is definitely from the converter. If the unit is solid state, there are ways to reduce the hum, namely with condensers, but I'd have to see the circuitry in order to recommend how. www.tubesandmore.com sells power transformers that will work on most world voltages and will work from 50 to 60 cycles. As far as I know, most power transformers that work at 60 cycles, will work well at 50, but may get a bit warmer. One that is underbuilt, and already runs hot at 60, will definitely get too hot at 50. Where real trouble comes in is when you operate a 60 cycle phonograph at 50 cycles. The records will play too slow. From what I've read in the past, though, a simple shaft converter (size reducer/increaser, depending on the frequency shift) was added to correct this problem for items sold overseas. With this in mind, it seems to me that the motor coils themselves have no trouble with the lower frequency. I assume, then, that power transformers won't, either, unless you make a drastic shift and operate them at 25 cycles (or anything below 50 cycles).

Thomas

Thanks for all the input guys, and sorry for not keeping up with a reply--this project got put on hold for a while...

Anyhow, I ended up concluding via some lab tests that the main hum was due to running the original 60 Hz transformer at 50 Hz, which was causing a small amount of resonance in the transformer plates themselfs which fed through the circuit. Rather than bothering with messing around with that beat up old thing, I simply got a new one made--250V in, 117V out with a 6.3V tapping for the heater circuit--and it now works like a charm! Almost.

There is now one more hum, which I *think* I know what it is, but am not sure. Basically, if I crank up the bass level, it hums. The hum is louder at higher gains, and sounds like it's in the 50Hz range... Any idea how to track down what this might be?

I know pictures / circuit diagrams would help, so if anyone wants to help out but may need some more info, just email me at bms8080 AT hotmail.com.

Many thanks in advance!