Heater Issue Solved?

[xtian]

With all tubes in and maxxed, no guitar, I get a slight hum and hiss with a slight motorboating sound (flapping).

Does the motorboating go away as you dial the volume down?

With only a guitar cord, (no guitar), the hum is outta control.

You know you can cause any amp to make angry noise if you plug in a cord with no guitar attached, right?

With guitar plugged in, minimal hum, but I get a loud hissing sound and squeal still.

Again, is there any useful range in the volume control, or is the squeal always there? Reason I ask is that I made an AX84 SEL and had similar problems. Both solved by reducing the input to the second stage.

When I tap on Pre1, the noise is much louder than when I tap on the side of the second preamp tube.

As it should.

The EL34 gets very hot, I don't recall it ever getting this hot too hot to touch.

After playing for less than a minute, it should get hot enough to burn your skin. Just make sure it's not redplating.

[surfsup]

Another update...thanks for helping me on my wonderful journey to amp bliss!

Does the motorboating go away as you dial the volume down?

Yes, with G1/G2/MV at noon, the amp sounds great. Totally playable.

u know you can cause any amp to make angry noise if you plug in a cord with no guitar attached, right?

Just posting all the info. I figured no guitar with a cable means the ground was broken and it would be noisy. I'm glad the amp is actually doing something it should!!!

or is the squeal always there?

All pots max except MV at 2pm or higher it squeals. MV lower with all pots max = no squeal. Maybe I need to reduce the gain at tube 2 as well, or stage two tube 1?

Amp Changes, I was hard at work today
-I moved the OT secondaries so they are not running under the PT cathode resistor/cap
-I removed and put back the 22k CC grid stop resistor, no change.
-I had the amp running and touched (finger) the yellow lead between coupling cap on first stage C15 and G1 pot and amp went nuts. I replaced the lead with shielded and grounded the shield as well. I ran shielded to G2 as well. Still no change though when I touch the shielded leads the amp doesn't complain.
-I shortened the three ground leads that go to chassis to basically zero slack (input jack, board, three prong). No change.
-I poked and prodded with a wood spoon for 20 minutes. No change.
-I swapped 5 tubes in the two preamp sockets. 2-ecc83S, 2-ecc803S and one ecc802. The 802 was a little less static but I figure that's because its a less gain tube. So in effect, no change.
-I disconnected the noval leads based on martin's suggestion hopeful that even though I wood spooned it and didn't notice any difference, it would help. I left the heaters alone thinking it won't matter (hum no longer a problem). No change.
-when I touch the ground lead off the shielded run from PRE2 pin7, the flapping/motorboating disappears or reduces (about 90% of the time but occasionally the motoboarding persists)

Symptoms:
I get hissing at all maxxed with no guitar, a little bit of hum.
All controls at noon amp sounds good.
I get squeal with guitar when all max and MV reaches 1:30-2pm

Man, I feel like I've built 10 amps and there's only one in front of me still not finished. I'm going to beat this though!

[xtian]

You may benefit from my SEL build log:

https://tubeamparchive.com/viewtopic.ph ... c&start=45

[martin manning]

-I had the amp running and touched (finger) the yellow lead between coupling cap on first stage C15 and G1 pot and amp went nuts. I replaced the lead with shielded and grounded the shield as well. I ran shielded to G2 as well. Still no change though when I touch the shielded leads the amp doesn't complain.

No need to shield them if you aren't going to touch them, is there?

I get hissing at all maxxed with no guitar, a little bit of hum.

This says there is probably no feedback related issues inside the amp. Some hiss at high volume is normal.

I get squeal with guitar when all max and MV reaches 1:30-2pm

Are you sure that this isn't just FB from the speaker to the guitar?

[surfsup]

I had the strings muted, standing as far as possible fro the amp and speaker. Seems to happen at the exact same setting on the mv dial.

The hiss is more than a little it is exponential at a certain point and is pretty loud , not playable at upper levels.

[img1000]http://chicagocadcam.com/ChrisHahn/PRE.JPG[/img]
[img1000]http://chicagocadcam.com/ChrisHahn/POW.JPG[/img]

[martin manning]

So you are only an arms length away from the speaker? Solid or hollow body guitar? Does it do the same thing with another guitar?

The lead from the MV wiper to the power tube grid is very long, and much of the length is unshielded. The green wire section is the most suspicious, but I don't know; you already said you have tried moving things around there. If you want to try an experiment, disconnect both ends of what you have and replace it with a piece of shielded cable going from the MV wiper to a 5k6 that is soldered directly to the tube socket lug.

[surfsup]

I had the guitar on stand with a towel over it to dampen the strings.

I ran shielded to the 5.6k on the socket vertically mounted. Its better. Static now with everything max is about as loud as if you were to make a hissing sound at talking level, maybe a tad louder. I can live with it.

New prob though...sigh...when i move g1 g2 from both being max, if i move one down, at about 90% a loud hum, metallic resonance starts and will continue through the range until i move the other gain lower than 90%. The metallic sound is subtle. There is also some popping, crackle with a guitar, singlecoil semihollow. The main issue is the pot rotation, i realize i will prob never have all of it maxxed, but i know the prob is there and its bugging me. Any ideas? After reading 5000 posts i have never heard of a problem like that.

[martin manning]

Do you have another guitar to try? Sounds like this one may have some issues of its own, or possibly it's the cable. How far is it from the speaker? Even if you dampen the strings the top of a hollow body can still vibrate and shake the pickups. Is the squeal gone now?

The part of the layout that still looks kind of ugly is the cathode wiring on the power tube. Between the purple and yellow wires there is what, 10" of wire there? If you are only going to use the EL34 you could lose the bias pot and all of that. Cathodes are not as sensitive as grids due to much lower impedance, but you can still drive the tube from there.

[surfsup]

I agree the purple wires are a problem but I wood spooned them and they are also nearly identical to another build that is silent (claimed by the builder). I also have another guitar, but before I tackle that I have discovered what might be a new problem, I hear talk radio (AM?) very clearly when checking voltages, see below:

EL34 PT, 2-12ax7 Pre's
EL34 biased at 52.5mA
46.3 elevation circuit, 6.6 between the pins

B= 206.5 VAC
B+ 238
B1 232
B2 225.6
B3 211.1

1-Preamp 12ax7 (ecc83)
1 125.9
2 0.9mV moderate hum, moderate radio - never had radio before
3 1.014
6 154 moderate hum, moderate radio
7 0.1mV radio is loud and very clear - this never did this before
8 1.5

2-Preamp 12ax7
1 225.8
2 132.6
3 133.5
6 132.8
7 -5.6mV
8 0.753V

EL34 PTube
1 0
3 225.6
4 223.4
5 2.2mV moderate hum while testing
8 13.22

[img1000]http://chicagocadcam.com/ChrisHahn/PRE.jpg[/img]
[img1000]http://chicagocadcam.com/ChrisHahn/PRE_SIDE.jpg[/img]
[img1000]http://chicagocadcam.com/ChrisHahn/POW.jpg[/img]
[img1000]http://chicagocadcam.com/ChrisHahn/POW_SIDE.jpg[/img]

[martin manning]

Probably your meter leads are acting as an antenna, and then something is acting like a detector, such as a bad solder connection or even the point contact at the test point. Same with the hum... stray emf is picked up by the leads and fed into the signal path. Did you have the gain and volume controls turned way up at the time? Anything plugged into the input? Maybe now that the other noise is reduced you are able to notice this now? As long as you're not planning on measuring voltages while you're playing your guitar (and it doesn't happen when you're not), I don't think this is anything to worry about.

[surfsup]

Okay, I was wondering if I should go back to no grid stop on pin 7 tube 1 ... with the second pic, the resistor leads plus the terminal strip vertical metal solder strip, there is quite a bit fo exposed metal.

For the purple runs from the bias pot to the cathode resistor/cap if I shield them too, would that help? I have the OT secondaries right there due to the speaker jacks. The more I view this HO kit layout, the more I see it is not exactly optimal.

[martin manning]

The grid stopper on the input stage should help suppress RFI, in fact that is usually the main purpose for having it there. As long as you don't get radio with the amp buttoned up there's no problem.

The layout was better with the power tube one hole over. Re the OT secondary wires, a better routing would be to take them straight to the back wall and then bring them up from underneath the jacks. Once again, that is what the AX84 layout shows.

I'd get rid of the bias pot and the extra wire. I don't know if it will make any difference, but you could twist the purple wires together, and move the yellow wire from the board to the red test jack. It'd be a little shorter and it wouldn't have to pass over the OT wires.

[surfsup]

I ran the purple lead from the red tester to the pin and left the yellow where it was. This seemed the best. No change.

For the pot issue it is if G1 G2 are both max, and I turn G2 down leaving G1 max. The moment I turn G1 down a "hair" it goes away. The hum stops/starts with G1's wiper (see pic below) rotating up to the point where the dimple meets the same position as the pin 3 on the pot. Below that, the amp pops/crackles, and the humming disappears. This picture shows the dimple just below the rotation point where the amp pops into humming mode.

[img1224]http://chicagocadcam.com/ChrisHahn/POT.jpg[/img]

[martin manning]

A bad pot, maybe? What happens if you short the wiper to pin 3 when the pot is turned all the way up?

Re your new post about extending the OT wires... Given where you are now I don't think there will be any improvement, and I wouldn't bother. If you were using the socket hole next door, then it would probably be better to get those wires away from it a little more.

[surfsup]

I will try that, it didnt do it before, but i have to go to san antonio for work for a week...thanks for your help so far! I will check in when i can