[morzh]

Today the P-T156 interstage xfmr got back in stock at AES (Amplified Parts now).
Considering it is $16.50, and I've had to use that before on my 111 radio, it is a popular interstage for triodes, I ordered 3, and, when they offered free shipping for extra $18, I bought the 4th (sa price as the shipping) plus another 6.8uF cap I ordered anyway.

I saw the picture of the actual AK transformer...it is D**n awful. A wire core job.
   

I put a generator and the scope to see the frequency response of the one I have that survived, and....oh boy.
I will put it here after this post.

[morzh]

In order not to reinvent the tex I will put what I wrote on ARF.

So I went and looked at the transfer of the remaining good xfmr.
I fed it signal from 1kHz to 6kHz directly from my HP oscillator, while looking at the input signal directly across the Primary and at the output directly across the secondary. 

This is the setup.

The HP200D oscillator I havn't fired in over 10 years (restored way back).
   

The scope I fixed this summer with two channels. The channels are connected right across both windings, with the sig gen also right across the primary. So what we see is what is across the windings.
   


Now the inputs are in order: 1kHz through 6kHz.
Every photo will have the secondary to primary volts ratio (which is, more or less, should be the turn ratio, right? The claimed one is about 3:1)

1kHz - 0.65
   

2kHz - 0.7
   

3kHz - 0.825
   

4kHz - 1
   

6kHz - 1.66
   


So, so much for the promised 3.

I guess, the core type, the parasitics and the losses (what losses? 10M scope probe).

I feel justified replacing them.


PS. I was told that this is not the way to check an interstage.
Well, what I will do is, I have just ordered the P-T156 from AES, they will come in a week or so (free shipping USPS, you know) and I will repeat the experiment with something that has the modern core.

[morzh]

Put the bottom of the amp with the transformers into the freezer chest. Will whack it tomorrow.

Also, I followed Arran's advice and re-soldered the filament pins on those tubes that had bad filaments (3) and the P/G pins of the two that have good filaments.
No change.
The good filament tubes still have exactly zero plate current (the needle tries to move 1/3 of one division, which is the same as if it didn't move at all), and the other three never regained the filamet glow.

So, yes, failed tubes, not the solder in the pins.

[Arran]

Too bad Mike, but it was worth a try on a early brass based '01a, or any '01A for that matter. That set would have looked really nice with the brass based 201as in the island, well I guess it still can, but it will not play with them in there. The ones I have had the most problems with are low voltage tubes like #26s, #45s, and so on, high resistance at the pins for the tube filaments, and grids, really matters. Grid caps are a really high failure point as well, even if they haven't broken loose.
I read somewhere that the old trick for replacing audio transformers in A.K sets was to take an inductance coil used for a Western/Northern Electric 500 series desk phone, as they are wound the same way. I don't know whether there is a source of these other then robbing one out of a junk phone, and if one of the AES ones fits in the can, and works, well you may as well. I was going to mention the S.S sub for these, but since it's fairly collectable for a 1920s three dial TRF rather then some generic cheapie, the economics allow for using the iron.
Regards
Arran

[morzh]

The AES interstages P-T156 seem to be the choice of most folks who replace the AK original wire-core jobs, so should fit. Some people lay them on their sides, some, like that Glass Slinger ... lady? ... solders the bracket to the base. There seems to be enough space: the height of the base is 1.8" and the transformer is 1.2 or 1.3" tall.

[MrFixr55]

I have used the AES transformers in my AK10 Breadboard for a Pooley cabinet (10C), and in my 20 Big Box. They work, but distortion is high. (Of course, some of the distortion is from the grid leak detector, some from current AM modulation practices, etc.) I need to compare them to the ones from ARBE (He sells interstage transformers also). 2 years ago, I started to experiment with RC coupling but haven't gotten around to completing it. The reason for the transformers is because 01As, 26s and 27s did not have sufficient gain and I guess thy thought that transformers were better than extra stages. When the '40 came out, there was more interest in RC coupling, but 40s are very rare.

Someone on the ARF website designed a solid state transformer substitute. Here is a link to the thread.
https://antiqueradios.com/forums/viewtopic.php?t=342560

Sounds like a real interesting idea. to some, this may be heresy, but to others who can't stand distortion in music (like myself) it may be a licit option, especially if hidden.

[morzh]

Yes, Robert Lozier


https://kd4hsh.homestead.com/SST1D-01.html


As for the distortion, I am sure the transformer is not the culprit.
I've used that one before in Philco 111, it works just fine.
Let's not forget, AK10 is not exactly a Hi-Fi. Nor are even much better designed radios like the very much sought after AK82 and AK84. In fact they sound not that great at all. Plate detector and othe things.

[Arran]

The S.S substitute I was thinking of was in an old copy of the AWA Old Timer's Bulletin, and it was pretty much a drop in replacement using power transistors, so the B+ voltage did not matter. It seemed like a more economical solution for repairing a multitude of 1920s TRF sets that are not worth a lot, but should be saved anyhow.
Regards
Arran

[morzh]

In especially valuable sets I try not to use solid state substitute (SSS).
Thought they should work fine despite what that fellow on ARF professed saying the old wire-core transformer is far superior to anything, plus the transformer uses the fact it's primary could go above B+ (yes, it can, but I am not sure this is a great idea to use this, even though it can be used).

I am not inclined to saving these, but I will replace them with transformers and try to use no solid state in these, though I am not opposed to it out of principle.

[MrFixr55]

BTW, I believe that the transformers in the later A-Ks are similar to those in the A-K10. I had an open one in my A-K20 BB that was open. I hollowed it and it is physically similar to the ones I took out of my A-K10. The P-T156s fit both the AK10 and AK20. My AK10 and 20 both play loud and proud, but not something I like to listen to music on.

[morzh]

By the later AKs I meant the likes of 82, 84, 707, 808 and such.

It goes without saying those mid-1920-s triode based radios are not Hi-Fi, despite all our love.

Even Neutrodynes, like Philco's 86 or 87, also triode-based, have vastly improved sound.

Of course they also employed better speaker and 45-tube pushpull output.

[morzh]

So today I retrieved the amp can from the freezer chest.
The instructions were to whack it agains the concrete floor.
I thought of it, found it 1) inconvenient, 2) potentially damaging the can, 3) messy, 4) some unpredictable effects.

So I put it, still in bag, on two hard wooden blocks on the concreted floor, put another piece of wood on top and gently knocked on it with a hammer.

It came out without argument or much mess.
I vacuumed the frozen pieces of tar, put the block on the table and gently tapping onit with the same piece of wood, cleared most of the tar away.

These are the can before and after, and the two transformers after removing the tar. Plu some other piece that was there, I am sure it is bad, whatever it is.

   
   
   

[Eliot Ness]

Mike, you might want to look into the transformers sold by ARBE. They're more expensive, but at one time I determined they would work better in my Neutrowound than the ones sold by AES. Can't remember exactly why, but maybe place a call or email to them.

[morzh]

John

Yes, I saw the Glass Slinger mentioning in his (her?) video Pat (the technician guy from ARBE) sold him some and said they would work well.
However I have already bought some P-T165. I guess I will have to justify the expense and use them.

[morzh]

So, I know no one will ever see it.
Still...

The 2M resistor from the AK10 amp. It failed because inside it is two think metal clipped wrapped around carbonized paper. Well, it separated from one of the leads.
The extracting is real easy, way better than any tubular caps.

So, this is the resistor connected to the old leads. 
   

Potted/rebuilt
   

2M value verified
   

Before rebuilding, in place
   

After rebuilding, in place