Wonderland/JM100 build

[norburybrook]

Bulb measures 4 ohms.


what should I check on the HT, this is a completely new issue for me....more learning.....I hate this bit at the time...


marcus

[martin manning]

So the bulb has continuity but doesn't light. Disconnect the filament winding leads then see if you can power up with the the limiter, on standby. Maybe adding the HT current going off standby was the last straw for the fuse. You don't have any of the dual voltage stuff in the scheme do you? The dog's demanding a walk so I have to break for a bit.

[norburybrook]

LOL, I've got the same issue here.... dog demanding a walk. I'll be back in about half an hour or so.

My power section is this;

wonderland power.jpg

with the bias I've got the CT not used. One side of the 23-0-23 going to ground and the other side to the rectifier board. I've got continuity to ground from the connection with the other side of the 23-0-23 and 1R. Is that correct? Is it connecting through the internal windings of the transformer?

I've just been continuity testing everything around the power section to find a short and that's the only place I got continuity to ground apart from the obvious ground points.






Marcus

[martin manning]

With the bias I've got the CT not used. One side of the 23-0-23 going to ground and the other side to the rectifier board. I've got continuity to ground from the connection with the other side of the 23-0-23 and 1R. Is that correct? Is it connecting through the internal windings of the transformer?

Yes.

I've just been continuity testing everything around the power section to find a short and that's the only place I got continuity to ground apart from the obvious ground points.

Your transformer wiring hould look like this (without the fuses, and the hum balance pot):

[norburybrook]

yes, that's what I have. except I've got the fuse on the white (240v) Tap, I don't suppose that makes any difference with AC

Peavy triumph 120W PT:
US version is: #70518719
European version is: #70518705

Primary:
0V Black
220V Grey
230V Brown
240V White

Secondary:
195V Red
0V Pink
195V Red

23V Orange
0V White
23V Orange

6,3V Yellow
0V Yellow


It's strange because I tested the whole power section first when i'd built it and it was all fine.

I've got it on the light bulb limiter at the moment with the filament supply disconnected from the valves and I can power up on standby but the power light doesn't come on. I've got 3vAc on each side of the bulb connectors. I'm reluctant to flip the standby switch as I now only have 2 fuses left!!!

Should the main HT be working on standby? i.e. the AC 190-(not connected)-190 ac to the rectifier? I've only got 4v AC at the moment!!


As I'm on the light bulb limited can I bypass the fuse, or is that dangerous for the transformers?


I've been through the whole amp and checked every connection on the boards and valve pins and there's no shorts to ground anywhere there shouldn't be.



marcus

[martin manning]

Don't bypass the fuse. Better to run out of fuses than transformers! Yes you should have the full B+ at the standby switch. Re the low voltage here's a problem:

[norburybrook]

thanks Martin,

that wouldn't explain the lack of power light and low voltage though would it, as that only comes into play once standby is in play? yes?

I didn't have that connected when I tested the power board and things were OK.

Any ideas why I've got no light and 190-0-190 ?

doesn't that suggest the transformer is iffy


Marcus

[norburybrook]

I've just been prodding and measuring things around the power input.

is this normal behaviour with the light bulb limiter?

When the amp is off but plugged into the mains I can read 240v AC across the live/neutral on the IEC neutral(0) and the live /fuse/power

When I power on I cannot get any voltage across the same live /neutral, well a very small one.

marcus

[martin manning]

Certainly with the reservoir wired as shown in the original layout you will have low B+... 220uF in series with 220k, and another parallel like that. I'm still recommending disconnecting all the transformer leads, measuring voltages on each winding, then reconnecting them one pair at a time.

[norburybrook]

OK, just so I'm 100% here.

primaries connected to mains.

disconnect the 190-0-190 and 23-0-23 and the 6-0

power up and check the voltages on those a pair at a time


yes?


marcus

[norburybrook]

Right with the center taps out of the equation as they're tied off I've got some strange results.

These are all measured individually to ground;

the 190 red secondary's are reading;

209 and 55 vAC

the orange 23-23;

7 and 26 vAC

and strangest of them all the yellow 6-0 heater tap is;

130 and 130!! vAC

now either I've done the measuring wrongly or the transformer is now acting up



marcus

[JazzGuitarGimp]

On the heater winding measurements, you're sure the meter was displayind 130V, and not 130mV ?

[martin manning]

Measure VAC across the leads, not to ground. Use some tape to separate the leads so you don't accidentally touch them together.

[norburybrook]

OK I've got 390 across the 190-190
45 across the 23-23
and 6 across the 6-0


so that's perfect then

Now what?

marcus

[JazzGuitarGimp]

Now that you have the heater secondary disconnected, you should do a few tests with your ohmeter; remove all the tubes and the pilot light bulb, then, at one of the octal output tube sockets, measure the resistance from pin 2 to chassis, then from pin 7 to chassis, then from pin 2 to pin 7. All three readings should indicate an open circuit; any hint of resistance points to a wiring problem.

Also, it would be a good idea (if you haven't already) to double check that all the electrolytic capacitors in the B+ string are correctly oriented (minus terminal to GND). And do the same check for the electrolytics in the Bias supply, where all positive capacitor terminals should be connected to GND.