HT1R Constantly Blowing Mains Fuse

Discussion - HT-1 amplifiers
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Posts: 2
Joined: Wed May 25, 2016 2:38 pm

Wed May 25, 2016 2:49 pm

Hi All

I'd like to run this past the group to see if it ring a bell with anyone...

My lovely little HT1R blew its main fuse (the one by the mains cable) the other week.

I got a pack of 10 replacement (250V 160mA as stated at the back), put one in and after about 3 seconds it blew. I coould here a bit of hum from the speaker then the light went our and nothing...

I opened up the back, disconnected the leads from leads from the transformer, put in another fuse and it was fine.

I connected hack the transformer and removed the valves - another blown fuse.

I removed the red leads from the transformer - no blown fuse

I put the red leads (HT i think) and another blown fuse.

My conculsions so far is that the problem lies with the HT part of the amp. I think that blowing a fuse with no valves in implies that the problem doesnt lie with the valves.

Does this ring a bell with anyone? Has anyone else had this kind of problem?

Thanks in advance


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Posts: 1160
Joined: Wed Jan 29, 2014 7:42 pm
Location: Virginia, United States

Fri May 27, 2016 2:33 pm

It could be any number of things. You can't rule out the valve since it could have failed and taken another component with it. If I had to guess (and this is a wild guess), the power tube failed and shorted the grid resistor. If that resistor is shorted, it won't matter if the tube is installed or not....but disconnecting the OT lifts the ground.

Again, that's a wild guess....bottom line it needs to go on a bench.

Posts: 2
Joined: Wed May 25, 2016 2:38 pm

Fri May 27, 2016 9:58 pm

Thanks - for your input - very appreciated.

I shall have a look and see if your guess is right or not. If I can find the grid resistor (i have found a circuit diagram), I should be able to see if it's shorted or not.

I want to be able to fix this - I hate the idea of having a dead amp that's not economically fixable.

I'll report back...

Posts: 31
Joined: Fri May 06, 2016 1:49 pm

Wed Jun 01, 2016 3:10 pm

I think it`d take some serious damage to make an HT1R NOT economically fixable !! ..

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