Wanted ads

Moderator: Capt. Black

BY lukewillasick
#855963
I recently bought an AC15C1 of trademe that in the listing the seller said the top boost channel wasn't working correctly.
I have finally picked it up and after reading about the issues that are common with these amps and hearing the sound of it I feel as though it is a faulty tube that is causing it.
Where would you recommend buying tubes from, I have looked online a bit, but thought I would ask for recommendations. Or alternatively, does anyone have any 12ax7's that they would be willing to sell.

Cheers
User avatar
BY Mike Clayton
#855967
Have you got another amp with a known good 12AX7? It might pay to "prove" the problem to a bad tube before splashing out on a full set. I just checked the schematic - it seems the Normal and Top Boost channels each use 1/2 of V1. Swap V2 & V1 (both should be 12AX7s) and see if that changes anything. Clean the input jacks too! :geek:
User avatar
BY Capt. Black
#856183
Mike Clayton wrote:Have you got another amp with a known good 12AX7? It might pay to "prove" the problem to a bad tube before splashing out on a full set. I just checked the schematic - it seems the Normal and Top Boost channels each use 1/2 of V1. Swap V2 & V1 (both should be 12AX7s) and see if that changes anything. Clean the input jacks too! :geek:


Even switching the existing ones around should work too, right?
User avatar
BY jvpp
#856189
I had the same problem. It was a faulty valve.
User avatar
BY Mike Clayton
#856192
Capt. Black wrote:
Mike Clayton wrote:Have you got another amp with a known good 12AX7? It might pay to "prove" the problem to a bad tube before splashing out on a full set. I just checked the schematic - it seems the Normal and Top Boost channels each use 1/2 of V1. Swap V2 & V1 (both should be 12AX7s) and see if that changes anything. Clean the input jacks too! :geek:


Even switching the existing ones around should work too, right?

Yes. Start by swapping over V1 and V2.
User avatar
BY jeremyb
#856197
Mike Clayton wrote:
Capt. Black wrote:
Mike Clayton wrote:Have you got another amp with a known good 12AX7? It might pay to "prove" the problem to a bad tube before splashing out on a full set. I just checked the schematic - it seems the Normal and Top Boost channels each use 1/2 of V1. Swap V2 & V1 (both should be 12AX7s) and see if that changes anything. Clean the input jacks too! :geek:


Even switching the existing ones around should work too, right?

Yes. Start by swapping over V1 and V2.


Or swap V3 as its only for the trem and reverb from memory??
User avatar
BY ToneLoungeMatt
#856204
We sell them, but like everybody else we are likely to be on shut down.

Just waiting to see if CourierPost will still take non essential parcels, but it is likely the tonne of orders we sent yesterday, will be our last for a while.
BY lukewillasick
#856243
Thanks for the reply's. I guess I'm going to have a while to figure out what the issue is. I will start by switching the existing tubes around and seeing what difference it makes.
I know that V3 says it is a phase inverter, is it safe to switch that one out with a potentially faulty tube, or is it best to only move V1 and V2?
User avatar
BY Mike Clayton
#856248
It won't hurt. But no point really - refer attached pic and fault-find in this order:-

1. Remove V1 & properly re-insert it. See if any improvement. If fixed then a badly seated V1 valve or dirty pins is probably the culprit. If not fixed go 2.

2. Swap V1 & V2 & see if any improvement. If fixed replace the bad valve (now in V2). If no improvement, swap V1 & V2 back & go 3.

3. Clean the input jacks. See if any improvement and if not go 4.

4. Disconnect & reconnect connector TCN2 from CON1 & properly reconnect. Check for improvement.

If none of the above you'll need a tech - it could be a bunch of isssues including a cracked trace on the PCB causing the intermittent fault.

AC15C1.jpg
AC15C1.jpg (129.28 KiB) Viewed 82 times