Kit 34 at it again

[pre65]

I second what Greg has said.

[Richard]

Hi Jiten,

Yes carry on with John's suggested list (of course!) but there are 3 secondary windings so you could do John's step 3) by removing the secondary wires one by one and checking for the fuse blowing each time you disconnected a wire. This may tell you where to look for the problem following that connection.

Referring to the circuit,

Removing the 5u4s should disconnect the black and white wires for the HT secondary but you have tried this and still have the problem so move on to;

remove one of the purple rect heater secondary wires and see if it still blows the fuse, if so,

remove one of the grey valve heater secondaries and see if it still blows.

------

"Also when I built the amp and tag boards again, I was getting a lower voltage which was possibly caused by lower voltage mains power. Could this have been an early sign of a fault in the transformer?"

Possibly or the circuit may have been under extra load for some reason which had dragged down the voltage suggesting a possible wrong connection or short.

[bob orbell]

I will have a bet that it is the bridge rectifier to the ECF80's gone short circuit, but DO carry out all the tests that John has given you. BOB

[jiten]

Thank you all. I like Richards idea as I then have fewer wires to disconnect. Will report back.
The bridge rectifier could have been problem as it was from RS and did not look that great.
as for system under stress, i had written down all the readings - memory you know, so if I can locate the note pad, will send the various voltages in case there is a glaringly obvious problem. As a matter of interest both the right and left channel seemed to be equal. So whatever the problem, it would have to be in the 'central' or common circuit.
Does that logic work?
Jiten.

[jiten]

Hi All,
I tried to follow the instructions so here are the results.
1. With 5U4s in place, disconnected one grey wire - fuse blew.
2. With 5U4s in place disconnected the purple wire - fuse blew. Grey still disconnected.
3. With 5U4s out and both grey and purple disconnected, fuse OK.
Where next? Reconnect one at a time and test?
Thank you.
Jiten.

[Greg.]

Oh dear, you need to follow John's instructions albeit you are getting there.

Hi All,
I tried to follow the instructions so here are the results.
1. With 5U4s in place, disconnected one grey wire - fuse blew. Not as instructed. Remove the 5U4's then retest.
2. With 5U4s in place disconnected the purple wire - fuse blew. Grey still disconnected. not as instructed. Remove the 5U4's then retest.
3. With 5U4s out and both grey and purple disconnected, fuse OK. Maybe you are getting towards finding the source of the fault, but do the above test properly and you should be in a better position to identify where your fault lies.
Where next? Reconnect one at a time and test?
Thank you.
jiten.

Sorry, not trying to be unhelpful, but it really makes sense if you accurately carry out John's instructions and not deviate from them. Thereafter, report back. I'm sure you'll get a positive response.

Greg

[Richard]

Hi Jiten,

Very interesting, look carefully around the 5U4 sockets/pins and wires for a mechanical joint/fault as the 5U4s are inserted.

Fit at least a 1.6A T fuse and confirm again that, with the grey and purple wires disconnected, and the 5U4s out, the fuse does NOT blow.

Then try fitting just one 5U4 at a time and switching on to see if it blows.

[jiten]

Dear Greg, Richard,John and Bob,
I have disconnected the 2 black wires, 1 white wire, 1 purple wire and 1 grey wire. Even with the 5U4s out, the fuse blows.
Power transformer or should I look elsewhere?
If it is the power transformer, where can I get a new one?
Thank you for your help.
Best wishes, Jiten.

[jiten]

Hi, Sorry for the slightly misleading message earlier. The fuse was NOT ok with the 5U4s in and the purple and grey wires disconnected. I just had not noticed that the fuse had blown. Sometimes it blows but does not leave a dark residue on the glass. I am running out of the 5 amp fuses so using the 2 amp T fuses.
Jiten.

[Richard]

Originally Posted by jiten

Hi, Sorry for the slightly misleading message earlier. The fuse was NOT ok with the 5U4s in and the purple and grey wires disconnected. I just had not noticed that the fuse had blown. Sometimes it blows but does not leave a dark residue on the glass. I am running out of the 5 amp fuses so using the 2 amp T fuses.
Jiten.

Hi Jiten,

Ok, no problem, so you've removed all the secondary loads but the fuse still blows.

I would now check all joints and connections from the iec mains input socket to the mains transformer. Undo any insulation tape or heat shrink on the primary wires and check you have good connection of the 2 primary windings in series for 230V operation. Check for any shorted strands of wire on the iec socket etc.

You should have the orange and red connected together, the brown to live, and the blue to neutral as in the psu drawing below.

If all is well with the connections and no short is found give it one last go.

If it still blows with no secondary loads connected then it does look like a fault in the transformer.

These were Morite design number 7502. You may find that on it to confirm. Morite are no longer trading but the designs were taken over by Amethyst. I had them do a Morite choke for me a couple of years ago and the result and service was excellent. I phoned them first, very helpful,

http://www.amethyst-designs.co.uk/
http://www.amethyst-designs.co.uk/morite/