Harley Benton GA5 head - Diagnosis

Took the GA5 to see Oli today, as he knows a bunch more about amps than I do and I was sorting and IDing a load of old (and I mean old) Warhammer stuff for him.

Turns out the problem is the power amp valve (EL84)... which it had occured to me it might be but without any other valves to test it with I couldn't be sure. Just glad it wasn't the power transformer really, as apparently those can be expensive.

So next thing is to get a new valve, I might replace the 12AX7 at the same time just so then it's full of all new valves. Oli tested it with Mullards, but I suspect those'll be a bit out of my price range.

Harley Benton GA5 head - It's alive! IT'S ALI- oh..

Time for the chassis out, valves uncovered test.

All plugged in, volume all the way down, power on... valves warm up and are glowing nicely so I slowly roll up the volume. And I get a sound! Strum a bit, and I get some decent clean sound, roll up the tone and the sound gets a little bassier... so far so good. Strum a few more times... and with a sound I can best describe as a 'squeak' the amp stops working again.

Hmmm...

Next step is giving all the components a quick once over, visually and with multimeter, just to make sure everything's okay.

After that, it's time to get reading because if there's not anything that's obviously blown up/melted/phased out of reality I really have no idea what's happened.

Harley Benton GA5 head - Power up and begin troubleshooting

So, with the chassis back in the box (probably unneccessary, but I did it anyway) I took the amp upstairs, plugged it into my 4x12, switched it on and... nothing. Not a jot. Not even a hiss or hum.

I know it's not a problem with the speaker cable or cab, as I tested them using my Peavey Road Master head just now and they work fine. So what other possible issues could there be?

I don't think it's the EL84 (power amp valve) as that was glowing quite happily when I looked in the back of the head. No idea if the 12AX7 was glowing as it's in a metal tube thing so obviously I can't see it. Next power-on test will be chassis out, valves uncovered so I can see them both. In the mean time I'm going to have a closer look at all the connections within the amp and double double check that nothing's loose or broken. Also going to bodge some means of keeping that in-line fuse thingy closed in case that's a problem.

Harley Benton GA5 head

Wow... turns out it's been nearly a month since I last updated this blog. That's mostly due to the fact I haven't really done any project stuff in that time. Which is lame as I still have that Swift LP copy to finish off.

Anyway, today I went to Bristol and picked up a non-working Harley Benton GA5 head for £10. The GA5 is basically an Epiphone Valve Junior with a tone control added and with the "Valve Junior" scraped off the PCB. I've had a look inside and can see no obvious problems (exploded components, loose wires, etc.) so tomorrow will power it up and see if it makes a noise. When I originally took the back off I noticed some kind of broken plastic thingy containing a fuse coming out of one of the transformers and thought that might be the problem but looking inside the wire doesn't connect to anything so I assme it's a bit of generic construction and whether it gets connected to anything depends on other factors (I suspect it'll be something to do with the country it's going to be used in).

Anyway, here are some pictures. It's not a bad looking little amp really. I've called it Bert.









Quite pleased with this really... needs a whole bunch of work doing; even if it did work some of the components probably aren't as good as they could be and I'm not sure I'm keen on all those floating resistors.