#124 Questions

[Bombacaototal]

Yes, I had never seen this before too, also tempted to compare using alligator clips.

Btw Marcus, I got a EVM12S and I am struggling with the push in thingys they have, really tempted to just solder the wires...any advice on how you wired/installed them?

[rootz]

I can't see how this reverse polarity would work for every (if any!) reverb amp. I'd say it could work only when phase is not reversed by for example a reverb recovery or mixing tube.

Still, it wouldn't cure the hum. I've been reading a bit more about it from Chad from Two Rock on TGP. He states they already tried the numetal and it didn't work. He also mentioned the hum didn't get louder with the master volume going up, so it wouldn't matter much on a stage. It seems they have sorted this hum problem out in their more recent amps. I wonder how! Easiest would be to just ask Chad via TPG or mail someone at TR.

Martin, that would be a good idea IF horizontally rotating the pan 90 degrees works. First post of page 26:

Hi Martin, thanks, yes this is exactly one of the tests I did, placing the pan 90degrees to the PT (flat as it usually is inside the box, with half of it sticking our from the front as I removed the grill) with the output (red) side underneath the PT I have a lot of hum, if I place the input side (black) I have hum but less strong, If I place it vertical as of it was my grill cloths I have no hum at all.

So unless I'm misreading, reorienting the pt to stand up would cure the issue. Correct me if I'm wrong, I sometimes miss crucial info when reading posts...

[Bombacaototal]

What if the output end of the pan is at the opposite end of the box and rotated 90 degrees?

Just tested this, first with the input inside the head and then the output. I placed both on the opposite side of the PT, with the other half coming out. Both are noisy. Weird...

Thanks for the post rootz, yes master does not affect it, in the sense that it does not act like a ground loop would, whereby when you turn the master up it enhances the noise. But of course when increasing the volume of the amp the hum is more evident

How would I orient the PT as a stand up?

[rootz]

Find a proper way to test if the reverb is actually silent with the pt in standup position. I'd take the chassis out of the head and see if you could test fit the transformer with it's current winding but in upright position. You can put the chassis on your desk and elevate the reverb tank over it. MAKE SURE THE LAMINATIONS ARE GROUNDED AT THE CHASSIS when the transformer is on it's side/in upright position. Got zapped once because I used rubber grommets and forgot to ground the core. Safety first.

Anyway, my whole idea is for you to test this before unsoldering and ordering more parts that don't work/do the job.

The obvious thing to do is test if in standup position orientation of the pt does in fact still influence hum levels. My guess is that you get the least amount if it is on a 90 degree angle to the ot. Standard practice in for example Marshall 100 Watters.

[rootz]

Oh and test beforehand if you've got at least 144mm or 4.5" of clearance between the tank and the chassis when everything is mounted in the shell. You don't want to do al the work and find out it won't fit.

[Bombacaototal]

Got it Rootz, thanks for the suggestion, I guess this will be my last resort as it will be a pain to re install the PT, plus the added cost.

I was checking AN and Taylor uses lay down Fender style PT like mine. I have actually been trying to get a hold of him for a couple of weeks with no luck so far but hopefully he can help..

https://ampgarage.com/forum/viewtopic.php?t=29774

This is the chassis I got from him and he uses ClassicTone as PT choice too. His orientation of the PT looks similar to mine with the heaters (green) closest to the pilot side (wonderland attached).

https://ampgarage.com/forum/viewtopic.p ... e4#p402124

There must be something to make this work...

Also the Two Rock transformer set looks identical to mine, I would even guess they have custom ClassicTone ones.

[norburybrook]

Raphael,

Only thing you haven't tried is a different tank?

I had strange problems with my princeton reverb and eventually I tracked it down to the actual tank. I got a replacement and it was all 100% fine.

It was a new tank and there was nothing obviously wrong with it but it had a strange resonance that would feed back at times. Not exactly the same issue but it made me think a tanks swap would be pertinent to try as well before major surgery.



M

[Bombacaototal]

Raphael,

Only thing you haven't tried is a different tank?

I had strange problems with my princeton reverb and eventually I tracked it down to the actual tank. I got a replacement and it was all 100% fine.

It was a new tank and there was nothing obviously wrong with it but it had a strange resonance that would feed back at times. Not exactly the same issue but it made me think a tanks swap would be pertinent to try as well before major surgery.



M

Hi Marcus, thanks for the suggestions but actually I am going back and forth between 2 tanks (from TAD) during the tests, a 3 spring long grounded on input (black) and a 2 spring long grounded on the output (red). Each has a different brand of RCA cable too....

The issue with the output grounded is an intermitent high pitch noise which only goes away if I physically touch the pan...but I like having both on different configurations for the testings.....although sound-wise I prefer the 3 spring..

I have a third pan at home which I haven't tried on this amp but will give it a go just in case.

[rootz]

My mind is getting fuzzy here, losing the overview of what you already tried... that is quite a lost by now.

I’m also puzzled that others have zero complaints with the same kind of setups or iron used. I tend to agree that it should work properly like it is build. Otherwise we would see loads of topics about humming Sss’s and Wonderlands.

I’m starting to think maybe the stay magnetic field of your pt is unusually strong or big. How could you rule that out or test that??

[Bombacaototal]

I sent an email to Classic Tone, and they have an amazing customer service, always prompt and polite on the replies.

Their response below:

Sorry to hear your are having this issue. We have not heard of anybody having the same problem with our 40-18042, or any of our other ClassicTone transformers.

Our 40-18042 operates at levels typical of all of our power transformers, so any stray magnetic field is not any different. Also, 40-18042 has a copper flux band the significantly reduces this stray field.

The only solutions are increased shielding and component location. Make sure the reverb pan cables are well shielded and as far away as possible from the power transformer.

After looking on the internet, this seems to be a common problem with reverb pans in head boxes.

My Head Cabinet is from a 2017 Two Rock Classic Reverb Signature including their RCA cable and Reverb Tank with sleeve. My chassis is from Amplified Nation. Never thought this could go wrong

One additional information is that both 12AT7 or 5751 as the reverb driver tube will produce the same amount of hum, and the cathode of the driver as 2.2K or 820R will also produce the same amount of hum, therefore I don't think it has any relationship to the gain level of the reverb circuit (how hot the signal is getting into the pan). This is different than Chad's comment about TR.

The hotter the signal into the tank and out more hum. Its even more dramatic with our overseas amps.

https://www.thegearpage.net/board/index ... g.1332229/

I was reading through a post from 2012 about an EU voltage TR amp with the hum issue and the solution was to mount the pan on the back pannel, but with that leaving the tubes with not much room to breathe (cool down)...
https://www.thegearpage.net/board/index ... e.1091898/

[Bombacaototal]

Raphael,

Only thing you haven't tried is a different tank?

I had strange problems with my princeton reverb and eventually I tracked it down to the actual tank. I got a replacement and it was all 100% fine.

It was a new tank and there was nothing obviously wrong with it but it had a strange resonance that would feed back at times. Not exactly the same issue but it made me think a tanks swap would be pertinent to try as well before major surgery.



M

Marcus, I tried my third pan, from Ruby Tubes. They add an extra shielding underneath on the output side. Without the sleeve I also managed to push the pan further away from the PT. In this configuration with the .01uF cap across the return pot I have much less hum

The level of hum is much lower although there is still a bit. It still gives a bit of “headache” and ear fatigue, in the sense that there is instant relief once I turn the reverb pot all the way down. Not perfect yet but getting better!

[Bombacaototal]

What if you try a shorter pan (8-type)? Will remove the pan input coil further away from the PT.
Otherwise I still believe that a high pass filter (270-470p/1M to gnd) between output of the pan and grid(stopper) of the recovery stage might help to reduce hum.
Just my 2c.
Markus

Markus, I will take on your advice to try to get rid of the residual hum. My amp currently has a 220K to ground between the reverb return rca on the chassis and the grid of the tube. I think I will need a high value capacitor like 2200pF or 3000pF to get to the correct frequency, right!?

Another issue I am facing is regarding the pilot light. I always found that 6.3V doesn't glow very well, so I wired mine as 240V, but the glue of the jewel is melting with the heat, making it fall off..I had a couple that fell already...any work around this or my only solution will be 6.3v? I think the Fender style bulb (they call it T47 or #44, not sure) has T-3 1/4 (10 mm) bulb size and BA9s base. I will try to find a LED replacement.

For reference this is my narrowed down search.
https://uk.farnell.com/c/lighting-produ ... -1-4-10mm-

This seems to be one of the few that can opperate at suppy voltage of 230V/240V
https://uk.farnell.com/cml-innovative-t ... dp/1105183

This is the spec sheet
http://www.farnell.com/datasheets/1756532.pdf

I think the measurements will work on the Fender style pilot

[markusw]

Markus, I will take on your advice to try to get rid of the residual hum. My amp currently has a 220K to ground between the reverb return rca on the chassis and the grid of the tube. I think I will need a high value capacitor like 2200pF or 3000pF to get to the correct frequency, right!?

Yes around 2n2 should work. You even might try only 1n.
Edit: you won't need a high voltage cap here.
Good luck!
Markus

[markusw]

Another issue I am facing is regarding the pilot light. I always found that 6.3V doesn't glow very well, so I wired mine as 240V, but the glue of the jewel is melting with the heat, making it fall off..I had a couple that fell already...any work around this or my only solution will be 6.3v? I think the Fender style bulb (they call it T47 or #44, not sure) has T-3 1/4 (10 mm) bulb size and BA9s base. I will try to find a LED replacement.

For reference this is my narrowed down search.
https://uk.farnell.com/c/lighting-produ ... -1-4-10mm-

This seems to be one of the few that can opperate at suppy voltage of 230V/240V
https://uk.farnell.com/cml-innovative-t ... dp/1105183

This is the spec sheet
http://www.farnell.com/datasheets/1756532.pdf

I think the measurements will work on the Fender style pilot

At a first glance I don't see a reason why these LED bulbs shouldn't work.

Markus

[beasleybodyshop]

Maybe not super helpful Post Facto but if you recall the Silverface Fender Showman-Reverb:

https://i.pinimg.com/originals/40/9d/42 ... 714cbd.jpg

There is a reason this thing is so tall.

When I built my first JM Sig amp clone I used a cab with bottom to top depth of 11", and I could hear some hum from the reverb pan no matter how I oriented the noise.

The next one I built, I ended up building the cab 13' tall and the reverb noise went away substantially.

You could maybe short the input of the reverb tank and see if the hum goes away. If it does, could be an issue with the reverb driver picking up noise - Fender used to mount these at an angle. You could maybe try unbolting the reverb transformer and rotating it while the amp is on and see if the noise diminishes?