About tube amp power transformer help

[fretzburner]

Hi I have an old japanese guyatone hybrid amp(ss preamp/tube power amp) and it's 100volts.I was thinking maybe the power transformer is multi input becasuse it has 4 wires and 2(shorted) connected to the fuse and the other 2(shorted) connected to the switch.How to determine if it's 220v ready? Is there any kind of measurement to check the 4 wires primary?
Thanks

[Jered]

  Look up the data for the power trans. online. That will tell you if there are 220 volt primaries and hook up info

[fretzburner]

No info about the transformer,been searching the net but no info.checked this site http://jacobs-online.biz/understanding_transformers.htm  and found some info about dual input transformer.saw the 4 wire primary and connected in parallel makes 110v and series makes the input to 220.maybe same with my transformer.Please have a look for clarification.
Thanks

[amptramp]

Japanese electric power is 100 V at 100 Hz.  Even if you had enough primary windings, you wouldn't have enough core to go to 60 Hz.  You need a new transformer.  Hammond has some, but they are pricey.  But the last time I ordered a Hammond transformer, I ordered through Washburne Electric.  It seems that electric supply houses get a discount and my $44 Hammond transformer came in at $38.  You may be able to cannibalize an old piece of electronic equipment for the transformer such as a TV or audio amp.

[R.G.]

First question: was it Japanese for sale in Japan, or was it intended for export? If it was for sale in Japan, it may be set up for 100Vac, the Japanese standard. If it was for export, it is almost certainly two 110Vac to 120Vac primaries that can be rewired in series. Do you have, or can you find, the schematics for the amplifier? That may simply tell you the answer without all the mucking around I'm about to tell you to do. I *think* that there is no reason for a Japan-only power transformer to be wound with two primaries in parallel.

Japanese electric power is 100 V at 100 Hz. 

That bothered me, because I once had to specify transformers for world wide use. I went and looked it up: http://www.japan-guide.com/e/e2225.html
It's 50 or 60Hz, 100Vac.  It is almost certain that Japanese manufacturers make their transformers suitable for 50 Hz so they will work in east and west Japan. So the frequency is OK, but the voltage is too big (120 vs 100).

@ OP:
If finding the service literature fails, I suggest some **very** cautious testing. If you decide to do the following, remember that touching the wrong thing can electrocute you. Only try this if you already know how to do it safely.

1. Make sure the equipment is unplugged from the AC power line.
2. Take a good digital picture or make good diagrams so you can put it back the way you found it.
3. Unsolder the transformer primary wires, labeling them as you go. Simple number labels (1,2,3...) will do. Do the same for the secondary wires, noting where they are connected as you go.
4. When you have all the transformer wires unhooked, use your ohmmeter to find out what wire belongs to what windings. For instance, you probably will find that the four primary wires are connected internally as two windings; perhaps 1 and 4  and then 2-3, just picking some numbers out of the air for illustration. Whatever they are, write that down. Do the secondaries as well. A single winding will have two leads connected by a low resistance, a center tapped winding will have three leads. More than three is a multi-tapped winding. Whatever they are, write down what connects to what.
5. Obtain a source of 60Hz ac, like an AC-output wall wart. 12Vac would be ideal.
6. Make sure the windings are NOT touching anything, just hanging out in mid air where you can measure them.
7. Connect the 12Vac wall wart output to one of the primary windings. Measure the voltage across this winding and write it down. Then go measure the voltages across all the windings, writing them down as you go.
8. Remove the 12Vac wall wart from the transformer, and get out your calculator.

The way transformers work is that every turn around the core has an equal voltage across it. So if one turn has 1/10 of a volt, then a winding of 10 turns has 1V and a winding of 100 turns has 10V total. You don't know the number of turns, but you don't need to. Since you measured all the voltages, you can calculate the voltage ratios.

The winding you measured first, the one you hooked up the supposedly-12Vac source to, forces all the other windings to be at their same ratios as if it were connected to the AC line. The 12Vac source was probably a bit higher, maybe 14V. The exact voltage doesn't matter.

Divide the voltage you measured on the powered winding into the voltage you measured across every other winding. It is likely that the winding that was connected to the AC fuse and switch in parallel with the one you powered will measure almost exactly the same voltage, so the ratio should be very nearly 1.0. Do the math on all windings.

When you have these ratios, multiply the ratios by 120Vac. The winding you powered will of course come up with the answer "120", since its ratio with itself is 1. Do this for all windings.

Then we reason about the results. I believe that the other paralleled primary will come out to 120Vac too, in the math.

One of the windings, the one connected to the tube heaters, will be very close to 6.3Vac if the amp has AC powered heaters for the tubes. This is your key for making the guess. If the heater winding comes out close to 6Vac, perhaps a bit high, then the primaries are probably 120Vac each, and can be paralleled on USA 120Vac fine. If the calculated result comes out more like 7.5Vac, then they are 100Vac primaries and you'll have to figure out how to power it.

There is a way to power 100Vac gear with 120Vac easily enough. You can make a Vintage Voltage Adapter to give the 100vac windings what they need, cheaply. But first things first. Do the test (CAREFULLY!), do the math.

[fretzburner]

This is the schematic found for this amp but this amp is for japan market marked 100v at the back plate.

jpg images
The schematic is obviously 220v and only 2 wire primary.My actual amp is 100v with 4 wires primary.Will check again later the wire colors.

R.G.- I will unsolder the primary wires first and will check continuity,resistance of the 4 wires.if found 2 separate windings,will connecting them in series doubles the input voltage? What bothers me to this is why they use 4 wires if this is intended only for 100v.Maybe they are using dual primary capable transformer.Right now i'm using 220v-100v step down transformer and the amp works fine.fender-like tone(fender tonestack).

[R.G.]

Actually, that clears things up quite a bit.

Power it on (safely!) and measure the heater voltages. When they're at 6.3Vac under operation, the primary voltage is right. If you're feeding it 100Vac and you get 6.3V on the heaters, all is well, and all you need to do is figure out how to feed it 100V, which is possible, and fairly simply.

If they're low, about 5.2-5.3, it would be OK to run on 120.

Um... are you in a 120Vac place? USA? Or do you get 220-240/50Hz?

[fretzburner]

I'm in the 220v part of the globe. Here are my findings as i unsolder the primary wires.i was wrong with 4 wires,it's actually 6 wires.

free upload

White and yellow tied together =A
Green and orange tied together =B
Red and brown tied together and connected to pilot lamp while the other terminal of p lamp tied to A
A and B to mains 100v

[PRR]

He's not going to find a lot of info on Guyatone. The same factory (the build-style is distinctive) produced Elk and post-1975 UniCord. They were a top-notch asian maker often imported as bottom-price gear.

> do you get 220-240/50Hz?

First post asks how to know if it's 220v ready?

So 220V juice is possible, tho not confirmed.

EDIT-- cross-post, be right back. Below is general process but I now have a specific answer for fretzburner.

> Power it on (safely!)

I would not, yet (unless it has worked this way on his power).

With utterly unknown primary, and a known 6V seconday, _I_ would start with a 0.6 V AC source. 1/10th of the known 6V heater winding. Get a 6V AC >1A heater transformer. Put 10 ohm 10W and 1 ohm 1/2W in series across it. Volt-meter the 1r resistor; this should have very-near 0.6V AC.

Pull all the tubes (so no heater load).

Clip-lead voltmeter to power plug prongs.

Clip-lead the 0.6VAC to the heater winding.

Stand back.

Power-up the heater transformer.

Now the power-plug voltage "should be" 1/10th of the primary voltage, the intended wall voltage. 10VAC means it is still wired 100V. 23VAC means it has been modded to 230V.

OK, let's be a little braver. Remove the 10r resistor. Wire the 6VAC through the 1r to the heater winding and back. Now the wall-plug voltage should be very-near the voltage you should run it at. Close enough that, if it is very near _your_ wall voltage, you can try a proper Smoke Test.

Put the tubes back in. Clip-lead the voltmeter to the heater circuit.

Stand back. Plug-in. WATCH meter!

If meter comes right up to 6.0V-6.9V, you are OK to play.

If it is headed for 12V or 15V, SHUT OFF FAST!!

[PRR]

This is 240V connection. Even if you have 220V, start with 240V connection. Measure heater voltage. If it is above 6.0V AC, it is plenty close enough for a 30 year old amplifier. If well below 6.0V, move that top wire down 20V to give nominal 220V.

[fretzburner]

Thanks PRR that was very fast. So my PT is really 220v ready.About the pilot lamp based on my measurement is it 120v? So i will have to connect it to half of the primary winding.Like in your drawing Brown to Red/Yellow.Is this right?About the voltages,just want to make sure if the higher resistance equals lower voltage(20v-8.3ohms/100v-1,6ohms) or reversed.
Thanks

[R.G.]

So my PT is really 220v ready.About the pilot lamp based on my measurement is it 120v? So i will have to connect it to half of the primary winding.Like in your drawing Brown to Red/Yellow.Is this right?

That's the safe assumption. If it happens to be a neon indicator, it may work OK on 120 and 240, but across the 100-ish connection s going to be safe for it.

About the voltages,just want to make sure if the higher resistance equals lower voltage(20v-8.3ohms/100v-1,6ohms) or reversed.

Good suspicion. If the windings are actually tapped primaries, and it looks like they are, my first guess would be that the higher resistance would be the 100V side, and the lower resistance the 20V side.

This is based on the winding practice of using wire size (and hence resistance per turn) that's nearly or exactly the same for a primary with a tap at 100V. The resistance is not exactly the number of turns, as the length of a turn varies as the diameter of wire on the bobbin increases, but it's an indicator. So I would suspect that you are right, the high resistance side is the 100V section, the low resistance the 15V side.

15V? Yes. The resistance ratio of the low resistance end to the whole resistance is about 16% on both windings, indicating (but not certainly) that this is a 100V/115V or 116V trannie.

So I'd go along with stacking them, with red connected to yellow, and 220/240 in across white and brown. Leave the pilot indicator across red to white. And as Paul said, watch it carefully  when you first turn it on.

I have a variac so I could bring it up slowly; I'm guessing you don't. You might consider how much you will ever work on AC power stuff, and if you will do much with them, consider making yourself up a light bulb limiter. These insert an incandescent light bulb in series with the incoming AC line, so faults make the light bulb glow, but it limits the amount of current that can flow into the circuit. It's a quick way to limit AC currents, especially for fuse-blowing incidents that don't leave you time to measure.

[fretzburner]

Good news it's working now.Measured all the secondary voltages with 100v primary then rearrange the primary wires as per PRR diagram for 240v.Supplied again with 100v primary and measured again the secondary voltages and the result readings were half or little lower than the initial measurements.So confident now that i almost made it right.Plugged to 220v and read again the secondaries,the readings were a little lower than the initial measurements.Maybe i should use the white and green as primary but i'll leave it that way for a moment anyway the amp is working fine now using 220v.The pilot lamp is 120vAc
Note: the HV before is 362v and after conversion is around 350v.

Thanks to PRR,R.G,amptramp,and jered for your help.

Next project:will build a 1 or 2 tube preamp for this amp to make it all tube.I wonder if the power transformer can handle the added tube(s).

[PRR]

> if the higher resistance equals lower voltage ... or reversed

SORRY!!  That drawing is WRONG!! As you guessed, I reversed the high and low voltage and resistance.

Glad you figured it out.

> build a 1 or 2 tube preamp for this amp

I will argue against it. I have *never* seen that model. While there is no great demand for this amp now, I've seen too many amps chopped-up, and don't want to lose too much of our heritage.

But it's your mule now, do what you want. Certainly one 12AX7 won't stress the (irreplaceable!!) power transformer much. Two may be a bit much.

[Gus]

I would leave the solid state section.  It looks interesting and might be worth more left stock.

Remember some Musicman amps are IC and transistor to the tube output.

[PRR]

> some Musicman amps are IC and transistor to the tube

Perhaps not the best example. Some of those MM amps sounded like 400-horsepower shavers; at least to my ears.

FWIW: I like that Guyatone "transistor" preamp. It reminds me a lot of a Yamaha electric piano preamp which had a "shine" that didn't come from the too-short strings. Cascaded FETs, with good supply voltage, with well-chosen gain structure, can be very nice. The tone-shaping is right out of classic Fender and Marshall thinking. Using a FET as the first stage should offer much lower noise (both hiss and hum).

I'm not so sure about the O.D. channel. Reminds me of the 2nd G Ampeg VT40's Distortion input (tube based) which was just a bad fuzz with zero soul. Maybe it's not like that. What-ever.... if an amp has a sweet straight input, there's all kinds of fuzz-up stuff you can put in front.

[fretzburner]

Thanks for some useful suggestions,already started to mod the OD section.will test it later.added one diode and changed some cap values.I also placed an fx loop so i can plug my preamp builds like the E1,Marshall clean and dirty channels.No fancy thing in the fx loop,just cut the signal right at the master volume out.Still need to be tested later.

[cab42]

Thanks for some useful suggestions,already started to mod the OD section.will test it later.added one diode and changed some cap values.I also placed an fx loop so i can plug my preamp builds like the E1,Marshall clean and dirty channels.No fancy thing in the fx loop,just cut the signal right at the master volume out.Still need to be tested later.

I have that amp as well. I have had similar ideas regarding fx loop and preamp as you.

A few years ago I tried to build the OD section on breadboard as a stand alone fx. I think experimented a bit with diodes and capacitors as well. It sounded pretty nice. I think I even made a vero layout.

On this swedish site you can find an article about the amp: http://binatech.se/index.php/forstarkare-a-modifieringar/guyatone-55-watt-hart-moddad?showall=&limitstart=

Regards

Carsten

[fretzburner]

FX loop works fine as i tested it awhile ago,placed a delay in the fx loop and sound is okay clean or over driven.my OD mod is a little bit in the fuzz direction.will experiment it again after a few days.transfered the reverb footswitch at the front together with the clean/OD and used an old marshall dual button footswitch.Everything is fine now except the od which i will experiment a bit.