OT:What going to happen if I match 200ohm amp to 16ohm speak

**gvasale** · May 18th, 2012, 04:51 PM

Just for fun, I dug out my 1970 Cramer catalog. Lots & lots of transformers then. Triad s149a, 3k ohm ct primary, 4, 8, 16 ohm secondarys. UTC HA 135 3k/5k plate, fro 30 to 1.2 ohms in 8 steps. Also Stancor too. Try finding that stuff today. But there is a company that does custom transformers out there. Cant remember the name though.

**Steve Schell** · May 20th, 2012, 03:31 AM

I don't know about this particular equipment, but many old theatre systems sent the audio signal from the projection booth to the speakers behind the screen at a high impedance to minimize losses in the wires over the long distance. Amplifier power was precious and expensive in the early days. The RCA systems routinely used a 250 ohm tap on the amplifier's output transformer, a passive two way crossover in the rack at 250 ohms, 250 ohm h.f. and l.f. lines out to the speakers, then then autoformers for both h.f. and l.f. set for the particular combination of drivers used in the system. Autoformers like these were used:

http://www.oswaldsmillaudio.com/imag...s/DSC_0691.jpg

**stéphane Rame** · May 20th, 2012, 12:30 PM

RCA 9472-A specs

http://2.bp.blogspot.com/-wMm__DlVvX...s1600/9472.jpg
http://2.bp.blogspot.com/-jKRgPOIlCs...00/xt3083b.jpg

St?phane

**aditya** · May 21st, 2012, 01:52 AM

A transformer is a transformer, and any of the types will do the job.

The basic difference between an autotransformer and a conventional one is that the autotransformer does not provide that important "isolation" thing between the primary and secondary, as both are part of the same common winding. But as a result of this they also gain in efficiency & cost as the iron-copper requrement & losses reduce by half. Capacitive losses and resonant points also diminish quite a lot.

The OP already has a conventional output trafo built-in to the amp and terminated at 200 ohms. So ideally speaking anymore isolation is unnecessary, and a suitable autotransformer should suffice the needs (if one finds one). But the UTC LS-33 that "AB" has sited is of very good quality also, and will do the job equally well if not more. May be it is a bit costlier compared to a similar but of the autotransformer variety.

**sanhanul** · May 21st, 2012, 10:02 AM

Originally Posted by Steve Schell

Amplifier power was precious and expensive in the early days.

http://www.oswaldsmillaudio.com/imag...s/DSC_0691.jpg

That is a good point. And This RCA transformer looks sexy

I believe UTC makes very good trans but the shape of UTC trans doesn't really fit to my tasts sometimes^^. And I feel the UTC looks kind of too big for my amplifier
hmm....

Thanks for the information...

**sanhanul** · May 21st, 2012, 10:49 AM

Originally Posted by aditya

Hello sanhanul,

What do you want to know ?

..... and the 200 ohm thing is for the long cable run from the projection room to the screen area. The sound should be good. The input is also trafo driven.....should be good quality type when they are of such an old era. Someone else may be knowing more about these.

Aditya

I am here to learn. I was very lazy in learning. I would just bring the amplifier to a technician and he will do the job. But the busy and proud technician would not take time to explain everything. Even though he say, I wouldn't understand if I am not ready.
After I meet Altec, I fell in love to it and I decided to learn more about it which I used to do and stopped when I was a kid. And I am learning a lot through friends like you.

Another thing. I want to know whatever options there are for the amplifiers I bought. Because I want to be sure I do the right. I had a very old Philips amplifier with high impedance several years ago. It came to me with separate matching transformers. But the sound was not right.

I don't have any information of the amplifier I bought. But I believe Telefunken had made very very good amplifers in old times. I hope I can see somebody who has successful experience with them.

Thank you for your help.

**RonSSS** · May 21st, 2012, 10:56 AM

I still haven't seen a schematic for the whole amp. Do you have one?
It appears to be a single ended pentode output.
If that is the case, you can change the output transformer to one that matches your speakers.
However, the amp may have global feedback and it would need to change if the opt was changed.
Transformers limit bandwidth as it is. Adding an impedance matching transformer at the output of this one is just going to make that worse.

I'm thinking that what you bought "could" work well for HI FI, but it's going to take a lot of work and will be real low powered when done.

Ron

**sanhanul** · May 21st, 2012, 02:21 PM

Originally Posted by aditya

Yes, you can use it with the 604s as a 1-WATTer. But you have to put a 250mA-Fast Acting-Fuse in the speaker-wiring. The sound quality should be good, as you are almost in a 'constant-current' kind of a situation here.

Actually these 'ohms' things are simply one of the ways to get the full power from the amps. This amp seems to be a 20 watt one. So, at 200 ohms load, it will give 63 volts at 315mA of current. Now this 'current' is the limiting factor as it depends on the gauge-no. of the output winding in the trafo. So 315mA is the highest amount of current which can be drawn. Now a 16 ohms load at 250mA will give 1 watt. The voltage (63volts) is not an issue as it depends on the volume-control setting.

Hi, I won this trans. I won them very cheap.^^ I just want to try them just for curiosity.
http://www.ebay.de/itm/ws/eBayISAPI....#ht_500wt_1287

I think I will go for the UTC trans too which AltecBest found .
BTW Will 1 watt be O.K to play my 604B though?

Kim JH

**sanhanul** · May 21st, 2012, 02:34 PM

Originally Posted by RonSSS

I still haven't seen a schematic for the whole amp. Do you have one?
It appears to be a single ended pentode output.
If that is the case, you can change the output transformer to one that matches your speakers.
However, the amp may have global feedback and it would need to change if the opt was changed.
Transformers limit bandwidth as it is. Adding an impedance matching transformer at the output of this one is just going to make that worse.

I'm thinking that what you bought "could" work well for HI FI, but it's going to take a lot of work and will be real low powered when done.

Ron

Hi Ron,
I don't have another schematic except for what I post here.
I thought these amplifier PP output power tubes. What do you mean it appeared to have single ended?

Actually I worried that too many transformers will degrade the sound quality.
It is kind a headache. I am not good at waiting and adjusting to get the best result^^. Hope I can make it sound, and for better, sound nice.

Kim

**aditya** · May 21st, 2012, 04:48 PM

Originally Posted by sanhanul

Hi, I won this trans. I won them very cheap.^^ I just want to try them just for curiosity.
eBay: Neue und gebrauchte Elektronikartikel, Autos, Kleidung, Sammlerst

I think I will go for the UTC trans too which AltecBest found .
BTW Will 1 watt be O.K to play my 604B though?

Kim JH

From the picture, it seems the trafo will work, as there are 200ohms & 15ohms taps. So try and see for yourself.

About driving the 604s via 1 watt, yes they are high efficiency drivers, and 1 watt here can give 100db+.
But don't use it with that "250ma-fuse-direct-connection-to-amp" method, as it was the wrong answer sent to you by mistake (as already mentioned in post#11).