65DRRI - reverb signal to noise getting weaker, feeding back more easily

noisepolluter

I'm guessing one or both of the reverb send/return valves is on the way out. Any recommendations for replacement? Will otherwise probably just go for JJs. Was also planning to install a TAD reverb tank at some point.

ICBM

If you prefer you can pre-emptively fix the modern Accutronics units so they don't fail.

Cut the plastic jumper blocks off the wires, solder the wires to the pins as close as possible to the bobbins, and use hot-melt glue to thoroughly cover the joints and support the wires on the bobbin so they can't flex and break the fine coil wires - which is what kills the tanks. It's always the return end which goes because the wires are finer, but I prefer to do both ends just to be sure.

DJH83004

If you are not a soldering wizard like IC, the last few TAD tanks I purchased did have the leads connected directly to the windings, thus eliminating the plug arrangement. HotRox in Nottingham supply them to save on overseas shipping from Germany, if that helps. Definitely try swapping the valves as first port of call, you can swap the recovery valve (V4A/B), with one of the pre-amp valves, unfortunately you will need another 12AT7 to test the drive valve.  

ICBM

Yes, the TAD/Ruby tanks are built correctly - which is why Fender have now switched to them. Accutronics have thrown away probably their biggest contract for the sake of saving pennies on construction cost, with a poor design change that should never have been necessary.

The irony is that Belton tanks also used to be made properly, but when Belton bought Accutronics they carried on with the Accutronics design and not the better Belton one.

noisepolluter

Balls.
The TAD reverb may indeed be deeper and lusher sounding than the accutronics but also substantially increases background hum - it's clearly audible on 3.

The ECC803s's really don't like the amp either. In V1 and V2 they make the volumes behave weirdly (minimum still audible, then going through a bizarre phase shift almost like a harmonic trem effect as you turn them up).

In V4 it just increases reverb hum without deepening the effect.

Thankfully it turns out V1,2 and 4 were actually JJ ECC83's that are only a couple of years old and haven't been thrashed.

So I guess I'll get a replacement TAD and hope this one was just duff, and also find out if I can exchange the 803's for summat else... standard set of JJ 83's and 81's maybe.

ICBM

Have you got the new reverb tank in the right way round? The output end must be at the opposite end of the amp from the power transformer or it will hum. (As well as the right way round in terms of the cable connections - the two ends aren't the same.)

It sounds like your V1 and V2 have bad crosstalk, that causes the odd phasing thing because the two halves are in series with a phase reversal.

Personally I would just avoid JJ preamp valves! I've never liked them, although their power valves are good. A JJ 12AT7 might be worth having for the reverb driver (V3) since it's not actually in the signal path and it is run quite hard, essentially as an output valve.

noisepolluter

Cheers John - I tried the tank both ways round - one was even worse! 
I did also try swapping the 12AT7's round which didn't make any appreciable difference- though they are both fender branded so probably stock 10+ years old. Might a more sensitive tank show up noise problems from a worn out reverb driver?

The one thing I didn't try actually is reversing the RCA connections - I just did red/red, white/white.

I haven't yet tried putting new 12AT7's in - looks like I can get some NOS JAN Phillips ones for only a couple of quid more than new production JJs so might be worth a try.

Would the V1/V2 crosstalk thing be caused by the valves or the circuit?

ICBM

noisepolluter said:

I did also try swapping the 12AT7's round which didn't make any appreciable difference- though they are both fender branded so probably stock 10+ years old. Might a more sensitive tank show up noise problems from a worn out reverb driver?

No. The noise is from the return circuit being amplified, so it's possible that a *better* V4 could show it up more.

noisepolluter said:

The one thing I didn't try actually is reversing the RCA connections - I just did red/red, white/white.

Make sure you have the right ends connected. The easiest way to be certain is to disconnect the RCA cables at the tank end, then with the amp on and the reverb turned up a bit, touch the tips of the plugs. The one that buzzes is the return and should be connected to the tank output regardless of the colour coding.

It's also possible that the grounding in the new tank is different from the original, even if it's supposedly the same spec. From memory the return is grounded to the casing but the send isn't. If this is reversed, or if both ends are grounded, it may hum.

noisepolluter said:

I haven't yet tried putting new 12AT7's in - looks like I can get some NOS JAN Phillips ones for only a couple of quid more than new production JJs so might be worth a try.

These are the best 12AT7s ever made, easily worth the difference.

noisepolluter said:

Would the V1/V2 crosstalk thing be caused by the valves or the circuit?

Mostly the valves I think - although on older amps, bad grounding at the cathode connection can do it as well. I'd be surprised if that would apply to a reissue.

noisepolluter

Okey cokey- I've ordered a couple of Phillips AT7s. They'll get used in any case and I'll have some slummy spares.

I'll try swapping the RCA connections tonight - presumably if the tank is grounded differently (is there a way to tell?) then it's a non starter?

ICBM

noisepolluter said:

I'll try swapping the RCA connections tonight - presumably if the tank is grounded differently (is there a way to tell?) then it's a non starter?

Not entirely, but it's a faff to fix.

noisepolluter

It looks like TAD sell them direct with different grounding options - might be the way to go if I can't get this one working and (assuming next step) replacement rules out a fault...

noisepolluter

Happy to announce in the meantime that I've tamed the ringiness and feedback susceptibility of the stock accutronics tank by fitting some grommets from an old short spring tank I'd forgotten to get rid of, and putting a couple of sticky felt floor pads between the spring tray and the outer casing. 

Much more controllable at 3-6 on the dial, less metallic overtones and far less susceptible to vibration from the amp. Still quite a surfy, bright reverb obviously, but definitely more pleasant and controllable.