Advice needed...

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The4thWatcher13
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Re: Advice needed...

Post by The4thWatcher13 »

Okie dokie, the Hammond chassis has arrived. I've only had a little time to consider how this should be laid out on the chassis and the circuit inside. While I was in storage I came a cross some old proto parts. Not sure if they'll be useful or not. The chassis is 6" deep, 8" wide & 2" thick. As I mentioned previously I also purchased some 47uF/160V axial caps, 3 or 4 of which could replace the multi-cap should another need to be added for the 6AV6 that was added. There should be ample real estate inside this chassis I think. The chassis has a rather robust plastic "scratch" cover on it which it seems is placed there so you can mark-up holes and do the work and not scratch up the surface in the process. I'm really not too sure where to start so I'm checking out pics of the work others have done on small amps first and reading all I can. Busy weekend but I'm back at it!
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TriodeLuvr
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Re: Advice needed...

Post by TriodeLuvr »

Ahhh - flea clips! Haven't seen those in years. You should definitely replace the existing multi-cap. It's a senior citizen. :)

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Re: Advice needed...

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TriodeLuvr wrote:
Sun 04/18/21 8:13 pm
Ahhh - flea clips! Haven't seen those in years. You should definitely replace the existing multi-cap. It's a senior citizen. :) Jack
"Flea-clips" indeed. I bought an organ repair company years ago and there was all kinds of super neat old stuff like this. There were a bunch of clips in the boards shown and I pulled out the schnockerd ones. They fit in there quite tightly indeed. Is there any drawback to using these? Not sure if there will be any reason to do so on a small project like this but I just thought I'd ask. Also, currently I've got the type of 9 pin sockets that you can't use shields with. I'm gonna order up the shielded versions. (Why didn't I think of this last week?!)
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Re: Advice needed...

Post by The4thWatcher13 »

One more thing... I'm wondering if any 6AV6 modifications/experiments with the current circuit would be easier to do now as opposed to inside of the chassis. Yes I've still got the super annoying heater wiring hum but...
Just a thought.
(well..actually probably 6 of one 1/2 doz. of the other so...)
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TriodeLuvr
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Re: Advice needed...

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The4thWatcher13 wrote:
Sun 04/18/21 8:53 pm

"Flea-clips" indeed. I bought an organ repair company years ago and there was all kinds of super neat old stuff like this. There were a bunch of clips in the boards shown and I pulled out the schnockerd ones. They fit in there quite tightly indeed. Is there any drawback to using these?
They need to be used with a proto board that has pads on the backside so they can be soldered in place. Not as sturdy as turrets, but there's no reason they couldn't be used on a small project.
Also, currently I've got the type of 9 pin sockets that you can't use shields with. I'm gonna order up the shielded versions.
I really like the standard J-slot US sockets and nickel-plated steel shields. Second best are the Russian ceramic sockets and aluminum shields (although they don't shield as well as the steel ones). The Chinese components sold by so many of the musical parts houses are garbage IMO.
One more thing... I'm wondering if any 6AV6 modifications/experiments with the current circuit would be easier to do now as opposed to inside of the chassis.
That's probably the last thing you'll ever need to do. The values used this stage are somewhat routine, and there's not much point to making changes.
Yes I've still got the super annoying heater wiring hum but...
Did you say you have a scope? If so, check the ripple to see if it's 60 Hz (heaters/grounding/shielding or 120 Hz (power supply ripple). Elevating the heaters is a good idea in any case, and it's easy to do.

Jack
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Re: Advice needed...

Post by JMPGuitars »

Belden Micalex sockets are excellent quality. By far better than the average ceramic sockets. Good ceramic sockets are expensive, and still easily damaged anyway.

These shields will fit over most standard noval sockets: https://www.amplifiedparts.com/products ... ple-colors

Thanks,
Josh
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Re: Advice needed...

Post by The4thWatcher13 »

Jack: Thanks for the info and recommendations. I'll be on that later today.
Josh: Thank you for the link. Those are actually the ones I ordered!
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Re: Advice needed...

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I cranked up the scope and started looking at the DC through the multi-cap toward the plates and screens and then the AC along the heater run but then I started hearing a quick tick, tick, tick, tick, tick..etc, that I've never heard before. This is without a guitar connected to the self grounding jack but a speaker is always connected. I've never run it without a load connected. I have a 8 ohm dummy load that I can use if that's better than a speaker.
Another thing I've been thinking about regarding the hum is that, in my readings, people talk about proper grounding. There are actually 4 separate points on the chassis that things are grounded to currently. I know this is a bad thing and have been considering a way to remedy it.
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Re: Advice needed...

Post by The4thWatcher13 »

This is the waveform that exists on the ground terminal of the speaker jack. Looks like 60 Hz. I'll have to poke around to see where it's coming from.
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Re: Advice needed...

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Several things can cause 60 Hz hum, as you already know. Grounding issues can be difficult to troubleshoot, especially in a one-off build that hasn't been vetted by previous builders. Before you go down that road, it might be easier to first determine whether this is the heaters. You can substitute a 6V DC source temporarily to check this. Four D cells in series should be enough to light the tubes for a test. Consider the batteries throwaways, the cost of doing business. :) If this fixes the symptom, the problem is either a defective tube that's coupling from the heater to the cathode, or it's pickup (radiation) from the heater wiring to the signal path. The former is more common than you might think. Many a good tech has spent hours trying to find the cause of hum when it was actually one of the tubes. Pickup from the wiring can be detected by moving the wiring around and noting changes in hum level. It's also possible the lack of a shield on the 6AV6 is to blame. You could wrap some foil around the tube and touch it to the chassis for a test. Don't forget, also, that aluminum shielding won't help regarding magnetic induction. If the 6AV6 is too close to the power transformer, you'll need a traditional iron shield. It would help at this point if you could post a pic of the chassis.

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Re: Advice needed...

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The4thWatcher13 wrote:
Mon 04/19/21 7:52 pm
Another thing I've been thinking about regarding the hum is that, in my readings, people talk about proper grounding. There are actually 4 separate points on the chassis that things are grounded to currently. I know this is a bad thing and have been considering a way to remedy it.
Read the ground scheme thread in my signature. Follow the scheme there.
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Re: Advice needed...

Post by The4thWatcher13 »

Sorry, I needed to change this around. I'm having a "day"!
I swapped around and clarified what was previously written and added pics.
TriodeLuvr wrote:
Mon 04/19/21 11:25 pm
...it might be easier to first determine whether this is the heaters. You can substitute a 6V DC source temporarily to check this. Four D cells in series should be enough to light the tubes for a test...
I have a regulated DC voltage supply on the bench (70V-1.5A), will that work just as well at the batteries? I'm assuming that you're saying replace the AC transformer for the heaters with the 6V DC, ..yes?
TriodeLuvr wrote:
Mon 04/19/21 11:25 pm
If this fixes the symptom, the problem is either a defective tube that's coupling from the heater to the cathode, or it's pickup (radiation) from the heater wiring to the signal path.
Did you mean ..."if this doesn't fix the problem"?
TriodeLuvr wrote:
Mon 04/19/21 11:25 pm
If the 6AV6 is too close to the power transformer, you'll need a traditional iron shield. It would help at this point if you could post a pic of the chassis.
The pre tubes aren't that close to the transformers I'd say, but most the of transformers I see in amps have "bell" housings and these do not.
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Re: Advice needed...

Post by TriodeLuvr »

Yes, use the bench supply if it will provide enough current. Remove the filament wires from the power transformer temporarily and power the tubes from your bench supply. See if this reduces the hum.

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Re: Advice needed...

Post by The4thWatcher13 »

TriodeLuvr wrote:
Tue 04/20/21 9:42 pm
Yes, use the bench supply if it will provide enough current. Remove the filament wires from the power transformer temporarily and power the tubes from your bench supply. See if this reduces the hum. Jack
Thanks Jack, I got it. But I'll have to pick up again tomorrow. I'm kinda fried for the day. Tuesdays...brutal! :|
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Re: Advice needed...

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JMPGuitars wrote:
Tue 04/20/21 7:19 am
Read the ground scheme thread in my signature. Follow the scheme there.
I've been checking out your link Josh and thanks! I've made some changes and it did improve a bit. I'm kinda toast today so I'll pick up again tomorrow (Wed) Thanks!
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