Would installing a choke help SE hum?

[bnwitt]

Ok, everyone forgive me for repeating some things from other posts. I just learned about display modes in this forum. I wasn't seeing some of the posts because they were collapsed.

[tubeswell]

Ok, everyone forgive me for repeating some things from other posts. I just learned about display modes in this forum. I wasn't seeing some of the posts because they were collapsed.

Nema problema - Sounds like we're all singin' a similar tune.

(BTW that stuff about Niagara Falls was a good analogy - I must go visit that place some day ).

[captntasty]

Bad news

Well, once again I am having issues with the voltages at the filter cap and from the 5Y3 - volume is pumping as it was. I'm frustrated and stumped. Would bad filter caps cause this - from soldering and desoldering them so many times have I cooked one of them? arrrrrrrrgh!

[bnwitt]

If you think you've ruined a filter cap (doubt it though) you should disconnect the amp from the wall outlet, remove all of the tubes except the rectifier, drain the caps by grounding one of V1's 100k plate resistors to the chassis for 20 seconds with a jumper wire or meter lead, de-solder each filter caps negative (ground) lead and then turn on the amp. With your meter on dc volts, check the disconnected ground lead of each cap to chassis ground and see if you get dc volts on any of them. This will show leakage if there is any. If all checks out, I'd strip that chassis and start from scratch with the wiring as all have suggested.

[captntasty]

Thank you all

Thank you all for your posts. It seems there is much work to do on this amp. With the problems it's having I am going to leave it alone for a while I wonder if the PT is shot, not getting enough voltage after the rectifier - I'm really pissed off and frustrated. Thanks again......

[tubeswell]

Yep troubleshooting can go on for a while sometimes. Anyway so now you have nothing to lose except your patience right? What would be good is a layout plan for how you would position the wires before you dive into it again. (Express Sch does a freeware layout program off the net for Windows. If you've got a Mac, JSchem can be used to do layouts). Follow the tips and think about the layout from scratch. While it would be handy to use the existing chassis, you might have to be prepared to change the positions of the trannies/choke and tubes. If I were you I'd adopt a standard fender type layout where the tubes are all on one side and the trannies are at each end (so the PT does not induce EMF into the OT). Have the choke in the middle but sort of off to one side, and align the iron in the big iron bits so that they are at 90 degrees w.r.t. each other and (if possible) screened from each other if they are in close proximity (see pic).

Wire the heater circuit in first keeping the wires twisted and tucked away from where the signal wires will be (see other pic)

Shield your input-to-grid wires (see 'nother pic)

[bnwitt]

I'm really pissed off and frustrated

Don't be. My first amp was a 5E3 conversion of an old electar amplifier. It hummed like the Mormon Tabernacle choir when its forgotten the words. I was a real newbie back then and had much to learn. I shelved the amp for almost a year, built several others from well established layouts and each one was better than the one before. By sticking to established layouts and copying their lead dress and component position, I learned what made a quiet great sounding amp. I pulled that amp off the shelf, gutted it and started over with my newfound knowledge. It became a really sweet quiet machine. I presented it as a gift to my ear nose and throat surgeon after he fixed my deviated septum. He still loves that amp and I am most proud of it too. Have patience. You'll get there. Mind if I ask what layout you used to build the amp? The extra pots and mini toggles are throwing me.

[captntasty]

This amp was a kit from STF Electronics - this was the Supercharged Champ. I originally built his normal Champ and was happy with it. I run a stereo setup so I use both. The chassis comes pre-drilled so layout is pretty much set. The extra pots are a Master Volume and tone control. The mini switches are for negative feedback and a 4ohm/8ohm output. I don't know what I have to do to troubleshoot this new symptom - pumping volume. I have tried multiple sets of tubes with no luck. The hum is now of secondary concern as the amp is not functioning properly.

[bnwitt]

So are you having a cyclical change in B+ voltage at the output of the 5Y3 pin 8 with no signal present or just when you play something?

[cminor9]

The extra pots are a Master Volume and tone control.

Master volume on a champ? Hmmm...

You'll get it. I had to strip my 5E3 (my first amp) out of it's old chassis and rebuild in a new one. That was frustrating. It's still not as neat as bnwitt's pics, but it's quiet.

It can be frustrating, but it's all learning. You don't build a tube amp if you don't want to learn, right? It'll be fine.

[captntasty]

cminor9 - thanks for the encouragement.

So are you having a cyclical change in B+ voltage at the output of the 5Y3 pin 8 with no signal present or just when you play something?

There is no change in the voltages either cyclical or on the attack of the guitar being played - the voltages are just lower than they were normally and the volume sporadically attenuates then returns to normal.

I am not sure where to start to trouble shoot this - test the PT? How do I do this? Would a component further down the line affect the voltage from the PT to pin 8 of the 5Y3? I'm not that experienced at troubleshooting and don't know what to test or how. Stumped. Anybody know of a place to start?

[tubeswell]

I am not sure where to start to trouble shoot this? How do I do this? Anybody know of a place to start?

Jack Darr book has a few good tips, and Chapters 1 - 8 are free on-line

http://www.pacificrecone.com/JackDarrBook.html

Try and figure out where its coming from by diagnosis - Are you getting low voltages on one of the plates or on all of them? One plate might indicate that one stage is the problem, and so on...

[captntasty]

Thanks tubeswell for the link - I'm going to look through that as soon as I post these voltages. I'm not sure which plate voltages your asking for so I include them all:

5Y3GT
pin 4 - varies -4.6 to -5.0VDC
270VAC
pin 6 - varies -5.9 to -6.3VDC
267VAC
pins 2,8 - I know these are filaments but this is the voltage I noticed had become lower 288VDC - was 305VDC. Not sure what voltages the others were at.

6V6GT
pin 3 - 272VDC
603VAC
pin 8 - 22VDC (cathode and beam plates)
47VAC

12AX7
pin 1 - 113VDC
230VAC
pin 6 - 111VDC
224VAC

Do these voltages tell you anything?

[bnwitt]

Ok, well first of all you should be measuring VAC on pins 4 and 6 not VDC. Measure each pin to ground first and then measure from pin 4 to pin 6. Pins 4 and 6 are the input of the rectifier from the PT HT secondary. Pins two and 8 are not only the 5 VAC heater supply, but pin 8 is also the output of the rectifier. You can measure VAC across pins 2 and 8 and find around 5 VAC and then measure pin 8's VDC to chassis ground and get your approx 380VDC. So on pins 4 and 6 each to ground you should get about 325VAC. Between the two pins you should see about 650VAC. On pin 8 to ground you should see in the high 300s or low 400s VDC.

[bnwitt]

Heres a doc file for you to fill in.