Hi all and thanks in advance for any advice you might have. I've been lurking for a while but finally have a question that I have not found already answered in the forums. I'm not sure if this is the right forum for this question, but the symptoms started following a capacitor replacement job (as described in the Definitive Cap list thread). I managed to swap them all out on my HD-130 Reverb myself without electrocuting myself and was feeling pretty good when it powered back up.
Under normal operation it sounds as good as it ever has (I've been the proud owner since around 2001), but something happened to the reverb: after the cap job, turning the reverb to anything above zero produces a strongly distorted signal, with no apparent reverberation. I don't often use it, but the reverb definitely worked before this.
Other things which may or may not be relevant to this situation:
- I don't often use the tremelo, either, but I don't recall it doing the doubling-over effect when turned past 5 before. Possibly it did and I just never noticed. Possibly I read about that feature on these forums while I was preparing to replace the capacitors and now I am just inclined to listening for it. I can't say for sure, but it definitely does it now.
- after I biased the amp and put the whole thing back together, I realized the 12AX7 tube was not installed during the biasing process. Does this matter?
- on what I believe is being called the Driver Board, there were two capacitors soldered in parallel that added to 150 uF (I believe a 100 uF and a 50 uF - though I cannot recall the exact combo). This is not something I've seen in any other posts and was guessing someone just replaced the original cap with what they had on hand at the time. I replaced with a single 150 uF.
- a red-plating event prompted all of this. Tubes were maybe 6-7 years old and seemed like they were doing just fine until one night when they weren't. I don't know how long the red-plating sustained. Could have been up to a few minutes. I was messing around with tuner pedal on (effectively cutting signal to the amp) for a bit and when I turned it back off I realized there was no sound coming out. Proceeded to fiddle with all the patch cable connections before finally taking a peak at the backside of the head. Immediately switched it off and unplugged it at that point. Maybe that somehow fried something on the reverb circuit?
Like I said I've never really used the reverb on this (it is actually my bass rig) and I could definitely live with the amp as it is. But at the same time I'm worried I messed something up that could cause me other problems down the road.
edit: added the red-plating info and moved the thread to the more appropriate forum (I think)
Were the reverb cables to the tank reversed? It's always a good idea to go back and re-examine all work recently done to the amp.
Thanks, but no: I took a
Thanks, but no: I took a picture before disconnecting them to make sure I would put them back in the same orientation.
Power Supply Voltages
It's hard to guess at what might be going on. A good place to start is measure the low voltage power supplies and ensure +/- 16V. Replace the zener diode regulators if the voltages are not right. -mgriffin
it was the 12AX7!
I was desperately scouring the internets for any clues to this issue and stumbled up on this video in which a Fender 68 Custom Reissue Deluxe Reverb was exhibiting the exact symptoms as my HD-130: https://www.youtube.com/watch?v=vMvmXoFrYBI
The tech's solution is to recap, which he proceeds to do only to find that the reverb signal is still distorted. In this followup video, he finds to his surprise that it was the 12AT7 tube causing the trouble all along: https://www.youtube.com/watch?v=7arHLnZgllE
I ordered a new JJ 12AX7 Long Plate and popped it in and problem solved! Whew!
Good job sticking with it. I love happy endings.
Thanks for the encouragement
Thanks for the encouragement and suggestions!