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

[Jazz P Bass]

Quote:"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. Looking at the schematic again, perhaps the base is higher voltage because the collector is connected to ground ? "

The 'case' of any & all TO-3 transistors is always the Collector.



If it was at Ground potential you would not have any B- Vdc.

[pinkjimiphoton]

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.

thanks for the advice and help, i think i'm understanding. i think i understand why it was reading so weird, when in circuit.
i will wire it back up and reinstall the transformer and see if i can get some better readings.

something has opened? hmmmm there's not much there in that part of the circuit... one side of the wind goes directly to base, the other has some feedback (i think) with the 470r and 4.7r 's come together.

question; should i take voltage reading with the power transistors in AND out? cuz if everything else in that part of the circuit checks out, i'm thinking maybe the lower t3 has gone open? i mean, other than the couple caps and resistors, that's really the only thing left. i didn't replace the 4.7 r's cuz they seemed to read ok when i disconnected one side of them.

wait a minute, dumb question again... could the big 5 watt 1.5 ohm r13 between the top one's e and the bottom one's c be open? i didn't change that one either, as i didn't think i should see much of a voltage drop reading voltages. was pretty much the same.

thank you guys all for helping me figure this out

[pinkjimiphoton]

Quote:"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. Looking at the schematic again, perhaps the base is higher voltage because the collector is connected to ground ? "

The 'case' of any & all TO-3 transistors is always the Collector.

[ATTACH=CONFIG]34061[/ATTACH]



If it was at Ground potential you would not have any B- Vdc.

it was reading as being connected to ground with the beeper on my meter.

so.... if the transformer seems ok until hooked up and the rest seems alright, should i take a leap of faith and try the fresh set of power transistors i have?

i'd hate to fry 'em, i found like, 7 of 'em on the web and bought a pair. so there's still a couple out there if need be.

thanks for the info on TO3 transistors, i've only worked with "normal" kinda small signal transistors in effects and stuff in the past.

[pinkjimiphoton]

10-4 on what you are trying to achieve


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.

thank you for the info and the idea of isolation... if need be, i can TOTALLY dig that.
i had thought about pm'ing rg and asking him, we're friends on the stompbox forums but i know he's a busy man and i don't wanna be a bother.
this way maybe someother guy like me can find the cure for this or something else because of the patient guidance being shown my rank newb arse
i will read up on them.

when i took the transformer out, i could not get a reading to the case from anything, so i will try and reinstall it.

i wanna revisit that r4 resistor too, cuz on the r7 side i'm getting a solid voltage, but on the other side of that 22k resistor i'm getting nada.

something weird there too.. but i was thinking the first transistor may not show much in the way of voltages without a load going in. but i would expect only a couple volt drop across that one resistor, not a drop in that magnitude.

sorry for my crummy descriptions. i am again, very grateful for the help

[guitician]

so.... if the transformer seems ok until hooked up and the rest seems alright, should i take a leap of faith and try the fresh set of power transistors i have?

If both TO-3 transistors test ok, then why swap them out? Don't use new parts to test with. If you hook everything up and some voltages look off, then you know what needs replacing.

[pinkjimiphoton]

If both TO-3 transistors test ok, then why swap them out? Don't use new parts to test with. If you hook everything up and some voltages look off, then you know what needs replacing.

that seems fair enough. i will go down and check it out, i'll have to look up how to test TO-3 transistors.
thanks again, i'm on it.

[guitician]

Basically you have four resistors forming a voltage divider across the B- power supply with taps for the transistor bases and secondary windings. The two C8 caps keep it in balance. You should see a symmetry in the voltages.

[pinkjimiphoton]

k, thank you.... gonna go downstairs and get to work, will post with results.

[The Dude]

...... 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......

All a bit confusing, but to be clear: This is a negative supply, so the filters should have the positive lead connected to ground.

[g1]

A note of caution about your meter measurements. Don't rely on your beeper unless you know exactly what it means. It can mean different things with different meters. For people trying to read this, it is much better to give a resistance reading in ohms.
Some meters beep on diode check mode, others in resistance mode. The threshold for the beeper may vary, so some meters might be <25ohms beep, others may be <200ohm beep. If it's for diode check mode, the reading will not be ohms, but voltage drop across the diode.
Unless you are just looking for continuity vs open, like when checking cables, it's best to use the beep as an indication to look closer and get an exact measurement.

[The Dude]

Some meters will also beep using the diode check function if there is enough residual voltage in the circuit. If you're going by your ears you'll think there is continuity. However, if you look at the meter's display, it will not show continuity at all.

[Jazz P Bass]

"Tool Talk".
You have to learn to recognize the limitations of 'diode check'.

I just checked my Fluke 77/BN & it will 'beep' on any resistor lower than 1100 ohms.
Looking at the display shows .660 when reading a 1100 ohm resistor.
Which just happens to be the upper limit (kinds sorta) of the forward voltage of a silicone diode.

Stick with resistance readings when looking for resistance.

For checking transistors diode check is nice to have.
The Base & the Collector and the Base & the Emitter can be 'thought of' as a diode.

An NPN (Negative Postive Negative) transistor can be checked by Red meter lead on the Base & the Black lead on the Collector & then Emitter.
The meter will emit a short beep if the junction is good.
A long beep indicates a failed (shorted) junction.

A PNP (Positive Negative Positive) is the opposite.
Black lead on the Base & the Red on the Collector & then the Emitter.

The Germanium transistors that you will be testing will be below the silicon .500 reading.
Maybe .300.

[pinkjimiphoton]

A note of caution about your meter measurements. Don't rely on your beeper unless you know exactly what it means. It can mean different things with different meters. For people trying to read this, it is much better to give a resistance reading in ohms.
Some meters beep on diode check mode, others in resistance mode. The threshold for the beeper may vary, so some meters might be <25ohms beep, others may be <200ohm beep. If it's for diode check mode, the reading will not be ohms, but voltage drop across the diode.
Unless you are just looking for continuity vs open, like when checking cables, it's best to use the beep as an indication to look closer and get an exact measurement.

yeah, i only use the beeper if i'm looking for continuity from one point to the next, i don't look at the numbers in that case. i just listen to see if the beep is there when it should be and isn't when it shouldn't.

sorry for any confusion.

[pinkjimiphoton]

"Tool Talk".
You have to learn to recognize the limitations of 'diode check'.

I just checked my Fluke 77/BN & it will 'beep' on any resistor lower than 1100 ohms.
Looking at the display shows .660 when reading a 1100 ohm resistor.
Which just happens to be the upper limit (kinds sorta) of the forward voltage of a silicone diode.

Stick with resistance readings when looking for resistance.

For checking transistors diode check is nice to have.
The Base & the Collector and the Base & the Emitter can be 'thought of' as a diode.

An NPN (Negative Postive Negative) transistor can be checked by Red meter lead on the Base & the Black lead on the Collector & then Emitter.
The meter will emit a short beep if the junction is good.
A long beep indicates a failed (shorted) junction.

A PNP (Positive Negative Positive) is the opposite.
Black lead on the Base & the Red on the Collector & then the Emitter.

The Germanium transistors that you will be testing will be below the silicon ,500 reading.
Maybe .300.

awesome. i will check them out when i get a chance, just got outta the hospital, allergic reaction to an antibiotic. ambulances suck

i only use the beep test for continuity, or to test diodes. i don't read voltages or resistances with it, i just use whatever range i need on the meter for voltage resistance capacitance etc.

thanks guys. hopefully tomorrow i can get back to this thing, i gotta take the nite off.

peace!

[pinkjimiphoton]

sorry, had a bit of an accident and was outta commish for a few days. ahh, the joys of being old...
anyways, will post back after i get back on my feet and get working on this thing again.
thanks for all the help!!
peace