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I made some progress: It seems to work properly as an amp now. Can't tell you exactly how that happened... wire jiggling and such. Still no sound when not bypassed. I discovered that the grid connection to V3 was being shorted to ground. The cloth insulation had disintegrated. I fixed that and still nothing. I am seeing ac voltage that is affected by the input pot as far as the primary of T2 - I don't see anything on the secondary or anywhere past that. I haven't unhooked the secondary leads to isolate them and check for signal. That's next I guess. I hope there is nothing wrong with T2. There is someone over at PSW right now who has an open secondary on T3: http://recforums.prosoundweb.com/index.php/m/477940/0/.

Thanks and Best, Ben
 
That's our other buddy in this thread; not sure why his tech is over there instead of over here.

You probably had a tube socket contact issue, or similar.

Pull V6 and try it that way.  Also confirm r9-r12 are correct for value and connection.  If you take a resistance measurement of the network, I can tell you what's up without disconnecting the windings.
 
I tried it without V6 and still nothing. r9-r12 look like they are doing what they are supposed to. They have been replaced at some point, though. I was thinking it might be easy, when replacing those resistors, to switch the green primaries of T3 around. would that cause what is happening? I wasn't sure where to measure for the resistance of the network. I measured from c6/t2 to t3/c8 and it was out of range. Thanks for all your help, Doug.

Best, Ben
 
c6/t2 to t3/c8 when set to on would measure the primaries in series.  If you have the same transformers as the one you just mentioned, I'd expect to see something close to 1k8. 

you should measure from the transformer end of r9 to transformer end of r10, which should be at opposite points of the loop made by the secondaries of T2/T3, and again, if same transformer set, see something like 1k3.  If you see nothing, the windings are open, either through a winding failure, or a misconnection. 

If you determine you also have an open winding, and it's the same type as the other, it may be time to have Doc wind multiple replacements as a group and see if there's any savings to be had in numbers. 
 
Ok, with the unit in 'on' but not powered, I measured c6/t2 to t3/c8 at 6k and the transformer end of r9 to the transformer end of r10 at 142k - so something is definitely awry... I'm thinking of unhooking T2's secondaries and checking it when it is isolated - If it is a wiring fault with r9-r12/T2/T3 then I can rule out that transformer as the source of the problem, and if T2 is bad, I will need to pull it out anyway...

Thanks and best, Ben

**Edit: Also, any reason I shouldn't switch those green T3 primaries around to see if that's the issue?
 
Switching those secondaries within the network around gives me nightmares; how do you know which is where?  Mark the living crap out of them.  You are messing with polarity and series connection, and I'd hate to try and figure that out later if I messed it up.  Only lift one lead at a time, and take a lot of measurements.  make a lot of diagrams based on your findings.  Don't just unhook them all and start trying other combo's, or you'll certainly be screwed.  Assume they are right for starters. 

Primaries sound fine, based on your first test.  Resistances sound different, but they are there.  See if you find roughly 3K apiece on each by itself. 
 
Ok, I lifted those green secondaries and switched them: no change. I marked those and left them disconnected. I lifted the yellow and black secondaries of T2 (along with the yellow and black primaries of T3, and those 150k resistors) and I was getting some low ac readings that were proportional to the input signal between the yellow and black secondaries of T2 - so that's good, I've got signal that far now, at least. Should I connect a signal to the yellow and black primaries of T3 and see if I am getting anything on the output? They are disconnected right now, as are the green primaries. If I do that, how should I connect those green primaries? I can't thank you enough for your help, I feel like I might be getting close to seeing some limiting and I am super excited.

Best, Ben
 
Here are a few measurements:

T2 secondaries:
black/yellow - overload
black/green right - overload
black/green left - overload
yellow/green left - overload
yellow/green right - overload
green left/green right - overload

T3 primaries:
black/yellow - overload
black/green right - overload
black/green left - 3.62k
yellow/green left - overload
yellow/green right - overload (weird meter reaction - rises quickly and then flashes)
green left/green right - overload

Thanks and best, Ben
 
are you certain of your combo's?  With 2 black, 2 yellow, and 4 green, it's really hard for me to tell what you've done here.  You should measure, for instance, each black to all 4 possible greens.  Same for each yellow.    I still assume overload means 'open'.  But it can also mean the reading is right at the decade changeover point of your meters auto range finding, and it can't decide which decade to land in.  If your readings are right, it suggests all your windings are totally hosed.  Try them all again, and if you arrive at the same conclusion within a particular possible combo (black/green for example), add a 1K resistor (or any resistor of 500 or larger) in series with the meter and try again; you may get a reading you can subtract the resistor from, having bumped across the decade line. 

With everything lifted, you could also hunt for tone appearing on the 2 secs of T2 with signal coming in c6/t2, and then put tone in at t3/c8 and hunt for tone on 2 pri of T3, which I confusingly or not think of as sec also, to keep the terminology of this pair of transformers straight.  1 pri, 2 sec. 
 
emrr said:
1 pri, 2 sec. 
Click to expand...

Let's use this as the standard to refer to them. That's not how I labeled them above, though, just to be clear. I re-checked those readings and they are all right with the exception of the secondary of T3's yellow/green right - this was the one with the weird meter behavior and it was, as you thought, at the crossover point of the meter's auto-ranger. It is ~3.5k, which makes it sound like T3's secondaries might be ok? They both read around the same. T2's secondaries, on the other hand, sound like they are ******, unfortunately. My readings for the secondaries are different from our friend's over at PSW, but looking in the manuals, the re-order numbers are different for T2/T3 in the respective versions. So, I guess at this point I need to check the T3's primary and start trying to figure out how to replace (hopefully only) T2. If there is a discount available to have Doc Hoyer wind 2 or more of the same transformer, I wonder if it would make sense to have him just do however many of the 26c-2 version of T2/T3 and I could use those instead of having him figure out my version and the other.

Thanks and best, Ben
 
it would seem very strange for T2's secs to both be fried, with T3's being okay, given the connections. 
 
Hey Guys,

Doc just quoted me $600 to rewind. The price may be a bit more palatable for a multiple order.

Thanks for the link over here Ben. I rarely get time to weed through the forums.


joe





 
Hi Joe,

It'd probably be worth knowing what he quotes on doing all 4 pieces, if you guys both need them.  I'm still unsure if you both have the same transformers or not.    Clay tells me you have part # (667)s604, which is what was on the 26C-1 I had.  The part # is obscured on my 26C-2. 

26C-1 measured about 1k1 on the primary, didn't take a meaningful reading of the secs. 
26C-2 measured about 460 on the primary, and 2.5K total across both sec.

It appears the inductance used is the real killer, if trying to find a modern sub.  Someone here somewhere was looking at some Lundahl something as a possibility for either the 26C or the 26W, and the inductance was much lower.  I'm not sharp enough to fully grasp the implications there, other than the vague idea that the varying Z within the network will affect the response, with L governing the available range of swing. 
 
I measured the primary of T2 at 3.12k and the primary of T3 at 3k - so it sounds like those are good. I pulled T2 and indeed, both secondaries are fried. It is the S228E which is what is listed in the 26C-1 manual. I'm not exactly sure how to proceed. $600 is a lot. I would be willing to do a modern replacement (or a vintage one) but I'm not even sure what I'm looking for besides the dc resistances of the windings on one that I think is good. I can run a signal in and check the voltage ratio, but that won't get me much closer to being able to identify a suitable replacement. Hmmm...

Thanks and Best, Ben
 
The inductance quoted in the manual is the most important, the DC resistance gets you nowhere other than guessing it's anywhere from 30-50K most likely. 
 
Look at the 26W manual specs also; maybe a clue in the right direction.  can't recall exactly what's there. 
 
So Doug noticed that the 26C-1 uses the S228E in three places and the 26C-2 uses it in one, which means two things: 1) since the 26C-2 uses a S228E and that manual is more detailed than the manual for the 26C-1, I now have the specs for the S228E! (It is 20k:40k + 40k), and 2) I can sub in my 'extra' S228E in the bridge circuit and replace that one with something more standard. I guess they were using an off-the-shelf transformer for the bridge section in the 26C-1 and started winding a special transformer for that application in the 26C-2.

Best, Ben
 

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