[morzh]

Bypass the vol ctl, see if the vol increases.

[Hamilton]

I want to thank everyone for their contributions to my issues with the radio. I feel rather foolish not knowing how to properly read my multimeter but I will get over that quickly. Lesson learned!

I will order the Hammond that Ron suggested and all the phorum members that assisted me I am in your debt. Thank you.

[MrFixr55]

Hi Hamilton, 

ALL of us have had our Homer Simpson "Doopf" moments.  I went nuts for 4 hours on my job once, after hours with no cell phones to Tech Support back in the day trying to get a program to work because I did not know the difference between a minus sign (-) and an underscore (_)  I have forgotten other examples in my life (Maybe they were too painful to remember).

The thing is that you provided enough info to get it figured out.  You have accomplished a lot in a short time!

[DaleHCook]

The issue is the speaker voice coil impedance. the resistance is 1.1 Ohm. If the impedance is 4 or 8 Ohm, then a transformer will be easy to find. If the impedance is much less than 3 Ohms, it may get interesting.

That is indeed the issue. Measuring voice coil impedance is not a simple matter. Even with the classic instrument used for the purpose (General Radio Type 1603-A Z-Y Bridge) the resulting Smith chart is not easily interpreted.

[DaleHCook]

What you are looking for is a transformer that will match 6K to 1 1/4 ohms.

We don't know what the voice coil impedance is - just its DC resistance. The approximate voice coil impedance is fairly easy to measure with the speaker mounted in the cabinet, but I prefer a more sophisticated measurement using instrumentation. From experience I would estimate a 3 to 4 ohm range for the voice coils of most antique radio speakers. The optimal plate-to-plate load impedance for a push-pull pair of triode-connected 42s in class AB2 with fixed bias is indeed 6,000 ohms (see the characteristics for the 6F6, which has the same characteristics as the 42 and the 2A5). Among universal output transformers something like a Stancor A-2855, A-3880, or A-3890 would work. I do not know offhand if their physical sizes are any smaller than the Hammond 125-D suggested by Ron (but can check if needed), but they are all rated at 15 watts so, like the Hammond 125-E, they may all be larger than the original.

[Ron Ramirez]

The Philco service data gives a voice coil impedance of 1.25 ohms for the H-13 speaker used in model 650 consoles (among other models).

The Philco service data also gives a load impedance of 5900 ohms. 6000 ohms is pretty darn close, I'd say.

See the Philco Speakers spreadsheet available here. This is based on Service Bulletin 180-B, along with other Philco service data.

[DaleHCook]

Ron -

Does the service data show at which frequency the impedance was measured? Is there any information about how it was measured?

[Ron Ramirez]

It shows plate impedance @ 400 Hz.

Please download and read the spreadsheet for more info. It does not go into further details such as equipment used for measuring, etc. You would have to ask a dead Philco engineer those questions...and dead men tell no tales.

[DaleHCook]

Ron -

I have had the spreadsheet for some time but forgot that I had it. I am still getting used to using the plethora of information here (most of which is on my hard drive for convenience). If that is the factory data it is certainly more than sufficient for me. Methods for impedance measurement were around before Philco was building radios. I am close enough to being a dead engineer to appreciate that.

I am currently still involved in a major overhaul of my shop for the first time in a number of years. When that is done I will make some time to measure the voice coil impedances of my Philco speakers and see how they compare with the spreadsheet - that is why I asked about measurement frequency.

The Stancor UOTs which I mentioned should do an excellent job of replacing the Philco OT by selecting the taps for 6,000 plate-to-plate ohms and 1.28 voice coil ohms.

[Ron Ramirez]

Dale

Understood.

Are Stancor replacement transformers still available? I was under the impression they, like so many old time parts manufacturers, were gone with the wind - and we now have only Hammond to choose from.

Also, keep in mind the OP (Hamilton) is in Canada, so that will make a difference when he orders something.

Oh, and your measurement of the Philco speaker voice coils will be good info to look forward to. Please start a separate thread on that topic when you're ready.

[DaleHCook]

Are Stancor replacement transformers still available? I was under the impression they, like so many old time parts manufacturers, were gone with the wind - and we now have only Hammond to choose from.

Ron -

I am an inveterate collector and hoarder of parts. I have a several NOS Stancor and Thordarson universal output transformers, as well as a variety of other vintage iron from those two and other iron manufacturers.

Oh, and your measurement of the Philco speaker voice coils will be good info to look forward to. Please start a separate thread on that topic when you're ready.

Will do. One of the shop improvements is my recently acquired General Radio 1232-A (transistorized) tuned amplifier and null detector. It replaces my old GR 1231-B (tube) amplifier and null detector. The 1232-A is for use with my GR 1210-C (tube) unit R-C oscillator and decades-long favorite GR 1603-A Z-Y bridge. The three together form an all-GR audio impedance measurement system covering 20 Hz to 20 kHz for any audio impedance/admittance from a short circuit to an open circuit. Another part of the shop improvement (not yet completed) is new cabling devoted to that audio impedance/admittance measurement system as well as new pegboard storage for that and other cabling.

I still have to find a place to store the new chassis stand which I recently bought from Simon Sharp. The quality and ruggedness are both superb. It will get its first use soon, and should blow away propping up an inverted chassis at an angle to replace caps.

Another upgrade in the shop overhaul is improved lighting for photographing projects. I needed something more than just the overhead LED replacements for the original fluorescent tubes. I am still working out how to place, mount, and scrim the two new LED lights, and I need a more versatile way to position my DSLR - all I have now is a bracket mounted to a floor joist so the camera is looking down on the bench.

[Radioroslyn]

A while back I got a 116B from Bob that needed an output transformer (uses a H-13 spkr). Dug around and found a Stancor A-3852. Matches from 4K to 14K pri and .5 to 122 ohms sec. Rated @ 18watts. Bottom tabs are a little closer together and the core is just a bit thicker. Overall I think it will make a good replacement for the original.

https://www.bunkerofdoom.com/xfm/STANCOR...EB/006.jpg

[MrFixr55]

Hi Hamilton, The values for primary impedance I got from my docs are higher than those quoted by Dale and Ron, but go with them. [Correction, 07/11/23- By "them", I mean Ron R and Dale, not the specs that I posted from the RCA and Tung Sol documents. Sorry for any confusion.] My info was from the RCA Receiving Tube Manual, but possibly at a different voltage. Ron and Dale are Philco Experts and have the documents to prove it (Speaker P/Ns, Specs, etc.). However, anything mildly close will be better than the open one that you have.

The one thing that you may want to try to do is to peel back the paper. In your pic, there seems to be a burn mark. I expect that connection#3 is the open one and the burn is under #4, but it also seems that the wires cris-cross under the paper. You may get lucky. However, a new transformer is better than an 87 year old one.

[DaleHCook]

The values for primary impedance I got from my docs are higher than those quoted by Dale and Ron, but go with them. My info was from the RCA Receiving Tube Manual, but possibly at a different voltage.

Which edition? In the 650 the 42s are triode-connected in a push-pull amp, and the load impedance also depends upon bias - in the 650 they have fixed bias. See RC-13 p. 129. It is the only RC edition with full characteristics for the 42. RC-11 and RC-12 have only partial characteristics. From RC-14 on you have to look at the 6F6, which has the same electrical characteristics as the 42 and the 2A5.

[Radioroslyn]

While your under the hood take a look at the 42 sockets. What you are looking for are burnt marks or carbon traces between pins 1 and 2. Pin 1 is at ground potential and 2 is at +300vdc and the ac signal. This can cause these high voltages to arc and damage the socket or the output transformer in extreme cases. When it arcs it will develop a carbon trace which acts like a low value resistor or short. That causes the hv to be shorted the ground through opt. The other side of the heater pin 6 is 6v above ground and pin 5 is at -20 something. Not to much of a chance of a problem.

I have this problem with one of my sets I think it was the 660L. Out of a dozen that I've serviced I've seen it once so it's not a common issue. But opt on the H-13 are. That's been about a 50/50.