no clue here... how can i identify a suitable transformer for an old kay 704 amp?

[Jazz P Bass]

Well, I can say that I am confused after reading those voltages.

(never heard the terms anode & cathode applied to a capacitor)

Look at the schematic again.

Here is the lead configuration of a PNP transistor.



TR3 top Base & Collector readings cannot be correct.

You keep overlooking R123 4.7 ohm to ground.
That is why the lower IT winding appears grounded.

[pinkjimiphoton]

Well, I can say that I am confused after reading those voltages.

(never heard the terms anode & cathode applied to a capacitor)

Look at the schematic again.

Here is the lead configuration of a PNP transistor.

[ATTACH=CONFIG]34045[/ATTACH]

TR3 top Base & Collector readings cannot be correct.

You keep overlooking R123 4.7 ohm to ground.
That is why the lower IT winding appears grounded.

i guess i'm being unclear.

in an electrolytic capacitor, you have the anode, or "positive" side and the cathode goes to "negative".... sorta. the cathode doesn't always go to ground, but it does always go to the outer "wrap" of the foil in the cap. i may be wrong with the nomenclature, i am far from an EE.

i know the base and collector readings are wrong on tr3 . it is the same reading as having the lower tr3 out of the circuit completely.

i realize the 4.7r to ground (and the 1.5r as well) should be effectively ground, but the issue is IN the transformer.

i again removed it from the circuit, and read the resistance of the coils. primary 160r or so, and both secondarys are reading around 18r.

the problem is there is around 20 ohms to ground with the interstage transformer on the lower winding to the case of the transistor. it still passes voltage under test from my meter... i have continuity on the primary and both secondarys.
there is no continuity between the primary or either secondary.
both secondarys show continuity from start to finish on both coils and show no continuity between them.
the lower secondary ONLY is showing a low level of resistance to ground. it should not be internally connected to ground at all. it beeps under continuity between the start and finish (as would be expected) but is also showing continuity to the metal frame of the transformer, beeping under the diode checker, and showing 23 ohms resistance to ground. the other side is above 20meg to ground, which seems to me is what it should be doing.

again, this is with the transformer connected to nothing, out of the circuit and sitting on my bench. the 4.7r resistors can't possibly matter if it's not connected to them

so i know the secondary is toast (the lower one) and probably why all the other voltages are so wacky. before the transformer went, the voltages were about half of what they're reading right now... instead of 35v b+ it was reading around 17.3v. i'd assumed (perhaps wrongly) that that was because one side of the transfomer can't develop a load cuz it's shorted to ground... no inductance possible. kinda like when ya pull the tubes out of a tube amp and the voltage can change.
i'm sure i'm probably wrong, i often am, that's why i'm asking you folks for help cuz it's got me beat.

to me, the only explanation is the transformer is shot. i wish i had written down all the voltages before it fried, so all i can go by is my dicey memory.

thanks for the pic, but i know which connection is which on a pnp resistor. in this case, all the tr's are listed, top to bottom, collector base emitter. the plugs the output transistors sit in show an e and a b pin i assume c is to the case. really weird, to me. i've never worked with these kind of transistors before, so i pulled 'em to see what's what. each tranny is marked e and b next to the two pins that aren't to the case of it.

so.... i'm still pretty much stumped.
the voltages are what i was getting out of it, but they're way off from where they were before the interstage transformer died.

maybe i'm confusing myself between the b and c on those output transistors ..... i'd expect the higher voltage (well, the bigger voltage potential) to be opposite of what i'm seeing..... i'd thought the c should be higher than b, but i'm an idiot sometimes.

question: if the transformer's secondary is shorted to it's case, would that make the b+ approximately double?

i don't think it's the rest of the circuit.

i don't see any connection to ground directly within the transformer secondaries once it's out of the circuit, so it's gotta be the transformer. or perhaps something else fried the transformer, but i won't be able to tell cuz i can't get the amp to pass signal past it.

i mean, if every other possibility has been exhausted, it's gotta be the transformer itself... so the question remains how do i find one? i don't think i know what to search for. the only interstage transformers i've found appear to be for tube amps, and the impedance of the coils seems to be about a magnitude of 10x bigger than what's in there now.

sorry to be so confusing. i appreciate the help.
peace!

[guitician]

You could try one of these... https://www.edcorusa.com/xsseries-2
But I don't think you have the electrical knowledge to adapt the circuit to a replacement. You can use Mercury Magnetics vintage rewind service for much more money.

[pinkjimiphoton]

You could try one of these... https://www.edcorusa.com/xsseries-2
But I don't think you have the electrical knowledge to adapt the circuit to a replacement. You can use Mercury Magnetics vintage rewind service for much more money.

the primary looks close enough for rock n roll, but the secondaries are about 100x too big, if i need 18 ohms and these are 1.8k. can i add a resistance in parallel to bring them down to what i need?
i don't know much about how impedance works, outside of replaceing stuff this is my first rodeo with this kind of circuit.

i'm aware of mercury magnetics but would hate to put that kind of money into this amp, if it were something vintage and really valuable to someone other than me, maybe.

i am not averse to (since it's already damaged) to ripping it apart myself and rewinding it if i have to. i'd think if i can locate the short and insulate it i could be back in business, as there's still continuity with the coil. if it's shorting to ground i'm imagining it would have to be somewhere near one end of the coil, and if it's not i would imagine i could rewind it with properish wire if i have to.

i'd think finding an appropriate replacement would be easier... (if i had a time machine to go back 50 years )

or last option, could i effectively just build a transformerless phase inverter circuit with a couple pnp's to couple the preamp to the power amp? if so, as long as the voltage is right and the input/output impedances are right that may be the easiest cheapest way to go?

sorry for all the newb questions, i appreciate all info and advice greatly

[J M Fahey]

the lower secondary ONLY is showing a low level of resistance to ground. it should not be internally connected to ground at all. it beeps under continuity between the start and finish (as would be expected) but is also showing continuity to the metal frame of the transformer, beeping under the diode checker, and showing 23 ohms resistance to ground. the other side is above 20meg to ground, which seems to me is what it should be doing.

again, this is with the transformer connected to nothing, out of the circuit and sitting on my bench.

UNLESS your benchtop is a sheet of metal and connected to chassis ground, don't understand how any part of that transformer can show any continuity to ground.

Besides that, please replace continuity statements (yes/no) with resistance numbers, which are more useful.

Continuity beeps only belong in checking cables, a fuse, stuff like that.

Not sure yet your transformer is dead, have a good look with a loupe under good light, besides some burr scratching wire enamel there's not many ways for transformer core/frame to short to any winding.

Just for peace of mind one more time reread each of 3 windings end to end resistance and resistance/insulation to frame, while sitting on a piece of wood/rubber/plastic/dry carpet and touching nothing else except meter probes.
Unmounted from chassis, of course.

IF lower (or any) winding shows some reading to frame, please post values from each end to it.

Absolute worst case, use the cool cabinet, chassis and speaker (transformer too) and build a simple TDA2030 based amp inside.

If possible, post some pictures, in and out.

Is it built on terminal strips or some kind of early PCB (I'd be surprised if they did, but it's not impossible).

[Jazz P Bass]

I too am totally confused as to the IT readings.
It's this, then it's that.

Push comes to shove, that circuit should have enough drive to work a speaker (for testing).

A simple drive test into a 100 ohm resistor will prove it out.

I never got a coherent answer as to why the top output transistor had a higher voltage on the base than the collector.

Troubleshooting 101.

[pinkjimiphoton]

UNLESS your benchtop is a sheet of metal and connected to chassis ground, don't understand how any part of that transformer can show any continuity to ground.

wooden bench top, JM. what i mean by ground is the metal mounting for the transformer itself. it's not shielded or anything, the bracket that mounts the transformer to the chassis itself is reading shorted to the lower secondary by my beeper and showing 23 ohms of resistance to the casing of the transformer... this is OUT of the circuit and disconnected from everything.

Besides that, please replace continuity statements (yes/no) with resistance numbers, which are more useful.

Continuity beeps only belong in checking cables, a fuse, stuff like that.

i posted the resistances, primary is 160.8 ohms, secondary 1 reads 18.1 ohms, lower one reads 18.8 ohms. this is reading the primary from input to output, and each secondary the same.
secondary 2, the lower one, out of the circuit and chassis shows a resistance of 23 ohms to the case of the transformer which would mount to ground.

Not sure yet your transformer is dead, have a good look with a loupe under good light, besides some burr scratching wire enamel there's not many ways for transformer core/frame to short to any winding.

the first clue i had thinking it was the transformer was the sound of the amp just before it blew, which was remarkably like a bad ot in a tube amp. certain frequencies only would make it freak right out, sort of in between f# and g on the low e string. every amp i've encountered over the last 30 years manifesting this has had a cooked secondary and needed replacement. once out of the circuit, they always show a short to ground... in my experience anyway with this particular issue. when the amp arrived its speaker was blown, which was a clue too that the amps output had passed dc, as the speaker reads open... usually dc across the voice coil will do that, again, only in my limited experience.
i have looked at it under a good light, the weird thing is it didn't show this path to ground originally. after the amp blew, and i went thru checking voltages etc i replaced pretty much every component in the amp with fresh ones... i didn't bother with the non electrolytic blocking caps as i didn't think it would make much diff and i didn't wanna change the tone of the amp too much.
i am a total fuzzface addict, and for me, only germanium will do for that kinda stuff. this is one of the sweetest little amps i've ever played thru, with that nice presence germanium has to the midrange without being so toppy like silicon.
sorry... rant alert, i love fuzz .... when i originally took the transformer out and tested continuity and resistance with my digital meter, i got about what i expected to find.... primary and both secondaries were passing signal and showing the same resistances shown above... 160.8 r and 18.1r and 18.8r respectively. i did NOT check for a short to ground at this point, as i figured it was good... no short between primary/secondaries, and no wires connecting other than start and end to any of the others. there are 6 in total. they all read good.
when i put the transformer back in the amp, that's when things started getting realy weird, and all the voltages went off. in some places, all i get is millivolt readings where before i had gotten decent ballpark voltages. some things seemed to suddenly be shorted to the chassis ground. i checked and rechecked and reflowed and replaced any suspect caps (i don't trust electros too much these days). everything is apparently right, right values, right polarities, and nothing grounded that shouldn't be.
that was when i pulled the transformer again and discovered it reads a 23 ohm short from the top of the lower secondary to the case of the transformer. so there's def a short. seems weird the short would be a higher resistance than the coil of wire.
but i don't usually use transformer coupling, and this amp is venerable and i'd like to respect it.
((ok, rant alert)) in this day and age imho too many people immediately modify everything they get... they spend say 4 grande on a nice les paul, then strip the guts and hardware off to "upgrade".... i see this every day. amps, guitars, effects.... but the problem is, these upgrades ultimately render all the future vintage gear as modified, there won't be anything vintage in 20 years at this rate. utility grade only.
so i try and always repair and replace with the closest components i can find... i don't care about so called "vintage" caps and other passives...my ears aren't that golden generally... but i hate to gut something that sounded this cool if i can repair it. i've repaired a LOT of stuff over the years that other peeps wouldn't work on anymore in my area, i'm one of them guys that will rebuild the guts of potentiometers and stuff.
so i really wanna make this thing live again. i'm not averse to breadboarding and building a solid state driver if i have to to replace this. i would imagine it could be done fairly easily with a couple transistors and passives if need be. but before i give up and gut it, i HAVE to try and save it.
if you heard the way these things sound, you'd understand.

Just for peace of mind one more time reread each of 3 windings end to end resistance and resistance/insulation to frame, while sitting on a piece of wood/rubber/plastic/dry carpet and touching nothing else except meter probes.
Unmounted from chassis, of course.

i will do this again as soon as i get a chance to get down to my shop, but i've done this enough times i can memorize the readings.
primary 160.8 ohms from start to finish, resistance to ground/frame of transistor over 20 megohms (as high as my meter reads)

upper secondary reads 18.1 ohms from start to finish, resistance to ground again over 20m

lower secondary reads 18.8 ohms from start to finish, however resistance to ground on this reads 23 ohms to the transformer case from either end if memory serves. that i would have to check on when i get a chance, but i believe it reads the same from either side of the coil.

IF lower (or any) winding shows some reading to frame, please post values from each end to it.

again, the only winding showing reading to frame is the second primary, and it reads 23 ohms to the frame from either start or finish wrap.

Absolute worst case, use the cool cabinet, chassis and speaker (transformer too) and build a simple TDA2030 based amp inside.

i would really prefer to leave it all germanium and original. i would probably sell it at a loss keeping it original before i'd turn it into a solid state chip amp hoping someone else could fix it.
i've built chip amps, some sound great, but nothing silicon sounds like germanium. and at this point i've got about 400 into it, the amp itself is worth maybe 200 or 250 so i hate to give up on it yet.

pretty sure i could build a solid state version of the interstage coupling transformer if i had to, which would at least let it still look pretty much stock. i have thousands of germ transistors, tho in this case i may concede and use some fets or something.
i mean, i've built something like 300 working effect pedals over the last couple years, and tho i am no EE i do know how to cook up some fun things on the breadboard by monkeying with stuff so i think i can handle it... maybe

If possible, post some pictures, in and out.

Is it built on terminal strips or some kind of early PCB (I'd be surprised if they did, but it's not impossible).

it''s all point to point on terminal strips, Juan. it is layed out and built almost like an old tube amp, it's (well, WAS... once i figure out the problem, i'll go in and clean it all up right now it's a mess from soldering/desoldering and stuff) a really beauiful little layout.

after i get some grub in me (laid up with yet another herniated disc) i'll gimp downstairs and take some pics to post.
thank you and everyone else for the help and advice.
peace!

[pinkjimiphoton]

I too am totally confused as to the IT readings.
It's this, then it's that.(

i don't understand what you mean. the readings haven't changed at all JPB (that's cool, cuz i'm actually JBP). don't let me confuse you between continuity (a connection between two points) and the resistance readings. the resistance readings haven't changed at all from what i posted. the VOLTAGES are wack, that's for sure... but when i originally had the thing working before this problem manifested itself, i didn't bother writing down the voltages at the time as i thought i was done with it. i do remember that they were approximately half of what i'm seeing now... b+ was around 17v negative. the half power supply was around half of that, about 7.7v negative.

Push comes to shove, that circuit should have enough drive to work a speaker (for testing).(

interestingly i discovered by accident hat if e and c of the output transistors are shorted together for a split second, the speaker will make a sound like putting a 9v battery to it. just a click. this happens with either output transistor, but it does it even if the transistors are pulled from their sockets. it's really weird.

A simple drive test into a 100 ohm resistor will prove it out.(

what do you want me to do, replace the speaker temporarily with the 100 ohm resistor ? or...? sorry, not following you here. i am not getting any signal from input to output. i can try injecting some with an audio probe, but whatever it is is effectively killing off the first stage of the preamp too. all the voltages have been weird and way off since the transformer issue has arrisen. that too seems to indicate the transformer, as, with no load on it, it can throw off the rest of the amp's b+ kinda like the way you will get a bit of a voltage rise if ya pull the outter pair of valves in a tube amp. or if ya pull all the tubes, the voltage will rise cuz there's no load on it. i'm thinking the short in the transformer seems to make the most sense.

I never got a coherent answer as to why the top output transistor had a higher voltage on the base than the collector.

Troubleshooting 101.

that's because i cannot give you a coherent answer because none of this thing is making sense. since this issue happened, everything is wrong. it appears the 2n554's collector is connected to the casing of the transistor, as the two isolated pins from it are labeled e and b and they match what the schem shows, and the circuit in front of me as per connections.
since the base on each of the output transistors is connected directly to the secondary, there's really not a whole lot OTHER than the transformer to go wrong, no? looking at the schematic again, perhaps the base is higher voltage because the collector is connected to ground ? i dunno man, i'm stumped that's why i'm asking for help, and i appreciate it greatly!

[pinkjimiphoton]

i will try and have pics for you guys within the hour. thanks for putting up with my ignorance, i am thankful for the help.

[guitician]

-17 on both sides of the top C8 would make me think that cap is shorted, but what about the -35 on the same node?

[J M Fahey]

10-4 on what you are trying to achieve

lower secondary reads 18.8 ohms from start to finish, however resistance to ground on this reads 23 ohms to the transformer case from either end if memory serves. that i would have to check on when i get a chance, but i believe it reads the same from either side of the coil.

Weird readings, that's why I keep asking for re re re re confirmation
1) that winding must be physically touching the laminations/frame somewhere
Detailed resistance readings might provide a clue.
2) if one end or the other, then one should show 23 ohms to frame, the other should show 0 ohms.
That's at least conceivable because winding ends have enamel scratched and soldered to plastic/cloth insulated wire, and such solder blob , might touch something it shouldn't.
3) now if both show 23 ohms to frame, then "somehow" centertap of that winding must be touching frame.
Please understand why many of us are struggling with the measurements you provide.
4) If transformer works properly, meaning, say, 12VAC applied to primary yield , say, 1 VAC at each secondary, out of phase, and each capable to drive, say, a 47 or 100 ohms resistor (proving there's some current capability, not just voltage) , then you can try an "Argentine repair" he he, (we never can order special hard to find parts so we must use what we have or kludge something) which would be to mount the transformer insulated from chassis (maybe on a raised piece of hardboard or hard plastic or with insulated screws and fiber washers or .... ) and keep the amp original.
4) worst case, I would unwind and rewind it, but I do have a winding machine; you might kludge one, worst case a hand cranked one.
Slow and boring, but watching some TV in the background (not much brain power needed to rewind, besides counting turns) can help
Doubt there is some suitable commercial offering.
AFAIK VOX type ones are meant for 30 to 100W amps, any would fit a 5W amp.
There should, because it's a unique amp, the very first SS one in the World, but who said Life is fair ?
R G Keen has studied driver transformers a lot (as well as other distinguished Forum members) , this might help:
http://www.geofex.com/FX_images/Salv...rmer%20Kit.pdf
http://www.geofex.com/Article_Folder...ransformer.pdf

Good luck.

[pinkjimiphoton]

it beats me. i just took the IT out again, and measured resistance and looked for shorts. and took a mess of pics. now i'm not getting that short to ground i was getting before. this is really weird.

question... looking at this schematic, positive/negative polarity isn't specified. is it possible i put the electros in backwards? to me, looking at how they drew this up, there's a shorter t shaped connection on one side, the other side is larger (on the schematic itself i mean) and it has sides going up toward the other.. i assumed that was the negative side, as in an electro the outter wrap is a shield and usually connected to ground or a lower voltage potential than the positive side. the smaller end is the positive side as shown in this schematic, correct? cuz if not i think i suddenly discovered my answer

anyways... here's pics.

the transformer is out of the circuit completely now and everything reads fine. no shorts. wtf?

primary is black and red. reads 160 ohms

first secondary is green and blue, reads 18 ohms

second (lower ) secondary is orange and brown. reades 18 ohms.

still stumped, as the other day my meter was beeping with it out of the circuit from the brown and orange wires to the case of the IT. not now. <smh>

trying to add pics, but seem to be haveing issues, so please bear with me

[pinkjimiphoton]

here's the first 9 pics, have a couple more still to upload

[pinkjimiphoton]

here's the other pics.

[guitician]

Yeah, the cap symbol has the "U" shape for the negative and is the case of the capacitor. You should try to get the correct voltage readings with the transformer in now that it's no longer "Shorted". Leave the speaker disconnected as your are just concerned with the amps DC voltage readings. DC resistances on the transformer tell you the gauge of the wire used and not much else. The fact that they read the same on both sec. is a good sign that nothing has cooked. When you said that the B+ was 17v instead of 35v when it was working tells me that nothing was shorted, rather something has opened.