Rickresource Rickenbacker Forum

I have an AC15 that I bought in the early 2000s. Lately when I turn it on I hear the "hissing" sounds for a few moments, and when I play the volume will sometimes change - i.e if I'm playing with a bit of overdrive, the volume and distortion suddenly decrease. I've been doing some research and it seems that I may have a bad preamp tube, so my question is:

Does this sound like the right diagnosis, or could it be something more serious? I'm thinking about ordering Ei's or EH's for replacements, but I don't want to order parts that don't solve the real issues.

Also, I would like to know more about my amp, like when it was made. I believe it was made by Korg - the name plate states "Manufactured in England" and the first two numbers of the serial number are "96" - does anyone know if this indicates that the amp was manufactured in 1996? Or could someone point me to where I could get this info (I have tried contacting Vox, but I've not received a response).

Thanks,

JR

It was made in England at the Marshall factory. Korg contracted to have the Vox line made in the Marshall factory for the AC30 reissues and the AC15s and others, but in 2004 they moved production to China because Marshall needed room for their own product. So from 1993 to 2004 is Korg made in England.

It is hard to say what the hissing could be, especially since it goes away as the amp warms up. It could be noisy tubes, bad resistors or caps, or dirty tube sockets. If you have known good tubes you can sub them in and see if the noises go away.

Jo: Welcome to the RickResource Forum. Yes, you have it right, 1996. I have a Korg AC30 from 1996 and it is well built.

I had a similar symptom and mine was tubes. Also, I would take a few seconds to clean the input jack as well. I had the exact same problem with a dirty jack in one of my amplifiers.

Go for the simplest explanation and rule that out first.

Great - thanks for the info!

The only other item I have with tubes is my Blues Jr., but I can swap similar tubes and see what happens. I was thinking that I should have spare tubes on hand anyway, so I'll probably go ahead an order a few. Any recommendation about where to get EI tubes?

I have had very good luck with The Tubestore and also with Antique Electronic Supply. Both have been most helpful and provided great service at a fair price.

Thanks Peter!

EI stopped making tubes last summer, and towards the end, the quality wasn't very good. They had trouble getting some special metals and chemicals, etc., so some of the later 12AX7 plates aren't even coated and are bare metal....so if you want to get some good ones, you need to go through a good dealer that pre-selects them. The grey plates ones are the ones you should get for the preamp tubes. Their EL84's are still good to get mostly anywhere. I'd suggest the Tube Store as suggested above, and also Angela Instruments is a good source. Antique Electronics Supply will be fine for the EL84's, but I wouldn't get the EI 12AX7 there as if you do you'll get the non-coated ones which will fail in some circuits.

Another nod for AES

According to Tubedepot.com, Ei are coming back and resuming production. According to Western Electric, WE has purchased Ei's tube assets (this was disputed by Ei's distributor.)

It is hard, but not impossible to find Ei tubes these days (their 12AX7 grey plates, 12AU7s and EL84s are my favorites of recently manufactured tubes.) I haven't dealt with them, but tube-shop.com is I believe the distributor and at last look had some number of Ei tubes available.

I did buy a number of Ei tubes last year from a seller on Ebay (at the time, at a great value- I think when I bought a handful of 12AX7s, he decided to double his prices.)

FYI: I have had very good results with Tube depot and with AES (tubesandmore.com).