18Watt.com

Dude, you're not going to believe what I just did. When I replaced R7 I removed it's respective 6CU5 and when I took these measurements I had forgotten to put it back again! It's in now and therefore my trended voltage at the supply side of the 6AV6 plate R is steady at +114. There was a small dip at about 4 min but after that the voltage has been steady.

I'm only trying to help you eliminate one possibility regarding the hum. R7 is a totally different thing, really just experimental and not related. Just so you know (in case anything weird happens down the road), operating the amp with only one output tube really stresses that tube. Essentially, it causes the single tube to attempt to flow roughly the same current that would have been shared by two.

The DVM graph as it is doesn't represent a sufficiently sensitive scale for what we need. We're looking for mV, not Volts. I'm not familiar with that model Fluke, but maybe there's a way to increase the effective vertical sensitivity. The total sweep time in order to see 120 Hz ripple across the screen won't be longer than 0.05 or 0.1 second.

Jack

You can always add filter caps on the rectified current. I remember doing this with my lamington reverb stand alone reverb unit... but sadly to no avail. Never found the source of the hum. But I ran it through the fx loop so the hum was minimal. You can't do this.. but no harm in adding 1 or 2 extra filter caps. Put those before you start extracting current for the circuitry. Don't forget separating them caps with 5 or 10k resistors of a high enough wattage.
Did you test if it's through the heaters? It's easily possible to check this ...

Inspecting/testing your heater wiring is a great idea. That is often a source of hum. I can't see your heater wiring from the low res photos, but it should be tightly twisted and not able to move at all. You may want to consider elevating the heaters and see if that helps with the hum.

Thanks,
Josh

+1 for the heater elevation.

In my experience, rectifying the heater supply generally introduces switching noise, which can be even harder to get rid of than AC hum!

Also in my experience, the number one cause of hum is poor grounding. I highly recommend referring to the article here on "modern grounding".

I have had really excellent results using a combination of modern grounding and elevated heaters, even with very high-gain amplifiers. No background noise at all!

TriodeLuvr wrote: ↑

Mon 04/12/21 12:25 am

I'm only trying to help you eliminate one possibility regarding the hum. R7 is a totally different thing, really just experimental and not related. Just so you know (in case anything weird happens down the road), operating the amp with only one output tube really stresses that tube. Essentially, it causes the single tube to attempt to flow roughly the same current that would have been shared by two.
The DVM graph as it is doesn't represent a sufficiently sensitive scale for what we need. We're looking for mV, not Volts. I'm not familiar with that model Fluke, but maybe there's a way to increase the effective vertical sensitivity. The total sweep time in order to see 120 Hz ripple across the screen won't be longer than 0.05 or 0.1 second. Jack

Yeah, I knew it wasn't good for that to happen. I've been reading up on grounding schemes as well. Gonna try some things today. I'll switch to a real scope as well. Good scope info, thanks!

Bieworm wrote: ↑

Mon 04/12/21 1:01 am

You can always add filter caps on the rectified current. I remember doing this with my lamington reverb stand alone reverb unit... but sadly to no avail. Never found the source of the hum. But I ran it through the fx loop so the hum was minimal. You can't do this.. but no harm in adding 1 or 2 extra filter caps. Put those before you start extracting current for the circuitry. Don't forget separating them caps with 5 or 10k resistors of a high enough wattage.
Did you test if it's through the heaters? It's easily possible to check this ...

I'll be checking the heater wiring today. The heaters for the 6AV6 are just run straight to the breadboard and back again to the amp! Probably not good. In regard to additional filter caps room is definitely limited in this thing so I'm hoping to have to add as little as possible, but if you gotta, you gotta. How is checking for "heater hum" an easy task? Thanks for the info and input.

JMPGuitars wrote: ↑

Mon 04/12/21 6:00 am

Inspecting/testing your heater wiring is a great idea. That is often a source of hum. I can't see your heater wiring from the low res photos, but it should be tightly twisted and not able to move at all. You may want to consider elevating the heaters and see if that helps with the hum. Thanks, Josh

I'll try to increase resolution for further photo submissions. It's a real cram job in this little amp but I'll take things one step at a time to try to isolate the problem. If I've got to elevate, I'll elevate. Levitate, even!
Thanks Josh

The4thWatcher13 wrote: ↑

Mon 04/12/21 11:47 am

Bieworm wrote: ↑

Mon 04/12/21 1:01 am

You can always add filter caps on the rectified current. I remember doing this with my lamington reverb stand alone reverb unit... but sadly to no avail. Never found the source of the hum. But I ran it through the fx loop so the hum was minimal. You can't do this.. but no harm in adding 1 or 2 extra filter caps. Put those before you start extracting current for the circuitry. Don't forget separating them caps with 5 or 10k resistors of a high enough wattage.
Did you test if it's through the heaters? It's easily possible to check this ...

I'll be checking the heater wiring today. The heaters for the 6AV6 are just run straight to the breadboard and back again to the amp! Probably not good. In regard to additional filter caps room is definitely limited in this thing so I'm hoping to have to add as little as possible, but if you gotta, you gotta. How is checking for "heater hum" an easy task? Thanks for the info and input.

First off.. take Josh’s advice on tightly twisting the heater wiring. It should be twisted over as much of its length as possible. Avoid heater wiring being too close to any other wires or components as much as possible. Also avoid them being able to move around.
For the check if the hum is in the heater wiring:
Desolder the heater connections at the first tube they reach after the transformer. Then solder 2 short wires at that tube socket, with the other ends stripped some. Connect the heater wires to those stripped ends with insulated alligator clips. Put the amp on and normally there should be the same hum. Leave it on and disconnect the heater wires. It takes some seconds for the tubes to lose the light in their filaments, but if the hum stops immediately when disconnecting .. then you know it's heater hum... if the hum persists for a few seconds, the problem is likely somewhere else.

I've been looking over the photos you posted, thinking about the additional tube socket. Even with a fair amount of metal working tools and options for bending and cutting sheet metal, it isn't evident to me how you'll add another tube and create an amp that can be bolted into a case. I think you'll eventually need to remove the output transformer and mount everything on a new chassis.

Just to present one option, Lloyd Pans sells square-sided aluminum cake pans that are 14 gauge (.063") aluminum with welded corners. This is heavier gauge than the thin stuff sold by Hammond and probably about the limit for working with hand tools. A 6" square pan in 2" or 3" depth is about $20. They have rectangular pans too, but they're probably much larger than what you need for an amp like this. Anyway, one of these pans would be an inexpensive option if you have tools like chassis punches and a step drill.

https://lloydpans.com/bakeware/cake-pan ... -pans.html

TriodeLuvr wrote: ↑

Mon 04/12/21 12:35 pm

I've been looking over the photos you posted, thinking about the additional tube socket. Even with a fair amount of metal working tools and options for bending and cutting sheet metal, it isn't evident to me how you'll add another tube and create an amp that can be bolted into a case. I think you'll eventually need to remove the output transformer and mount everything on a new chassis.

Just to present one option, Lloyd Pans sells square-sided aluminum cake pans that are 14 gauge (.063") aluminum with welded corners. This is heavier gauge than the thin stuff sold by Hammond and probably about the limit for working with hand tools. A 6" square pan in 2" or 3" depth is about $20. They have rectangular pans too, but they're probably much larger than what you need for an amp like this. Anyway, one of these pans would be an inexpensive option if you have tools like chassis punches and a step drill.
https://lloydpans.com/bakeware/cake-pan ... -pans.html

I've shortened and twisted the heater wires and there's a definite improvement. I also moved said wires around a bit which had an audible effect on the hum. I think case solved. So I'm taking your comments about re-mounting this nightmare into a suitable chassis quite seriously. As you can see it's kind of a cluster in there and I"m not sure adequate separation is going to be possible considering current chassis size. I'm sure I can lay this out better from scratch.
So my first move is always to storage where I may have a suitable candidate. If nothing's there then I'll "pan it"!
It's something I had actually thought about but hoped I wouldn't need to do. But if you're going to do something, do it right. And this point in the project is pretty much the right time too do it.
Thanks for the recommendation and link.

It's true the Hammond enclosures are only .04" thickness, but that's fine for such a small project. Use metal fender washers to mount your transformers for reinforcement. I'd prefer a welded chassis with a securely fitting lid over a cake pan for the same price.

https://www.hammfg.com/electronics/smal ... assis/1444

The 1444-862 is $14.62 without the lid, or about $22 with the lid. That's definitely worth it. The shielding the attached cover plate will give you is worth it alone.

Thanks,
Josh

JMPGuitars wrote: ↑

Mon 04/12/21 8:15 pm

It's true the Hammond enclosures are only .04" thickness, but that's fine for such a small project. Use metal fender washers to mount your transformers for reinforcement. I'd prefer a welded chassis with a securely fitting lid over a cake pan for the same price.
https://www.hammfg.com/electronics/smal ... assis/1444
The 1444-862 is $14.62 without the lid, or about $22 with the lid. That's definitely worth it. The shielding the attached cover plate will give you is worth it alone. Thanks, Josh

Thanks Josh, it's great to have options for this kind of thing. I found no suitable candidates in storage though I did find some parts that will be used. There's only one concern I have about the Hammond chassis';..that is that they don't have Silver-Kote™ and Dura-Kote™! What will I do if I over cook my amp? I'll have a hell of a time getting it out of the cabinet!
But seriously, I appreciate both suggestions. I'd love to see some photos of amps that have been built out of either. I'll look around the site to see if there are any here.

The4thWatcher13 wrote: ↑

Mon 04/12/21 8:56 pm

Thanks Josh, it's great to have options for this kind of thing. I found no suitable candidates in storage though I did find some parts that will be used. There's only one concern I have about the Hammond chassis';..that is that they don't have Silver-Kote™ and Dura-Kote™! What will I do if I over cook my amp? I'll have a hell of a time getting it out of the cabinet!
But seriously, I appreciate both suggestions. I'd love to see some photos of amps that have been built out of either. I'll look around the site to see if there are any here.

Ack, I didn't consider that, you might want to set an oven timer.

There's been thousands of amps and projects built with those Hammond chassis. There are also places that sell blank amp chassis in the $30 to $60 range, at .09" thick.

JMPGuitars wrote: ↑

Mon 04/12/21 8:15 pm

I'd prefer a welded chassis with a securely fitting lid over a cake pan for the same price.

Try one before you knock it. The corners of the Lloyd boxes are fully welded. The Hammonds are spot welded crap. I've used both, and the Lloyd product is far superior.

Jack

EDIT: And they do sell lids.

The4thWatcher13 wrote: ↑

Mon 04/12/21 8:56 pm

I'd love to see some photos of amps that have been built out of either.

8 X 16 Lloyd box:

JMPGuitars wrote: ↑

Tue 04/13/21 5:51 am

The4thWatcher13 wrote: ↑

Mon 04/12/21 8:56 pm

..I appreciate both suggestions. I'd love to see some photos of amps that have been built out of either. I'll look around the site to see if there are any here.

Ack, I didn't consider that, you might want to set an oven timer. There's been thousands of amps and projects built with those Hammond chassis. There are also places that sell blank amp chassis in the $30 to $60 range, at .09" thick.

For some reason I was having a hard time imagining what this would look like so I hit the interweb and now remember these chassis'. I've been thinking "in cabinet" style for so long I'd never really considered it as a separate head. Doh!
Thanks!

TriodeLuvr wrote: ↑

Tue 04/13/21 12:16 pm

Try one before you knock it. The corners of the Lloyd boxes are fully welded. The Hammonds are spot welded crap. I've used both, and the Lloyd product is far superior.

Jack

EDIT: And they do sell lids.

Lids too? That's cool. I only use professionally made chassis for my amps, I couldn't sell an amp made on a cake pan. Of course, I don't use the Hammond stuff for amps either. I only use Hammond for accessory things like attenuators, and test equipment, or pedals.

TriodeLuvr wrote: ↑

Tue 04/13/21 12:20 pm

8 X 16 Lloyd box:

Damn, that's sweet! I'll be ordering up something today for sure.

Hmmm... On the other hand, you could call your brand "Cake Amps" and make it your thing. Easy slogan: "These amps are sweet!"