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teletroy wrote:It's hard to tell , but it looks like you have 4 resistors on one of your power tube sockets and then two on the other one. and they look like they go to places that they shouldn't

wait are those for your heater v center tap? Even if that was the case, something doesn't look right. Your tone cap on the tone pot also looks weird- it's hard to tell if it's shorted out or not.

teletroy wrote:

teletroy wrote:It's hard to tell , but it looks like you have 4 resistors on one of your power tube sockets and then two on the other one. and they look like they go to places that they shouldn't

wait are those for your heater v center tap? Even if that was the case, something doesn't look right. Your tone cap on the tone pot also looks weird- it's hard to tell if it's shorted out or not.

The orange tone cap is a temporary 4300pF that I took out from another amp because I didn't have a new 5000pF. The leads were already cut hence why it is there and it is mounted like that.

The resistors on the first power tube are the grid resistor, screen resistor, and 2 x 100 Ohm filament resistors. I know its crowded in there but nothing is fouling anything else. As far as I know.

I'm still struggling with this.

What I did today was:
1. Dissconnect all input wires from all 4 jacks and wire in a single Cliff jack with 1M directly to one of the 68K input resistors and also a ground point on the one of the jacks. The symptom of very little gain was exactly the same.
2. I ran a short length of wire with crock clips from the input ground to various ground points.
3. I used the same link from all combinations of grounds to other ground points - no change.
4. I redid the mains ground, first filter cap and cathode resistor ground by bolting a high tensile 6mm bolt through the chassis, fitted with star washers and tightened the hell out of it. I was previously using one of the PT mounting studs and I was tightening the bolt close to the point of shearing - no change.
5. I did a bit more re-soldering of joints I had already re-soldered.
6. I chopsticked about but found no suspect joints.

I finished off by playing my 5F2-A through the 5E3 cab and speaker. That thing is a monster compared to the 5E3 which hardly even begins to purr.

What can it be?

I am really a newbie here, don't know a lot, but do you think it might be a bad capacitor? Voltages are ok, right?
Try rewiring pots... aaaa... just think of these things that you can check easily... hope that you'll find out soon - and if possible later post some clips when you finish
Cmon amp, it looks way to nice to be crappy!

Bulatovic wrote:I am really a newbie here, don't know a lot, but do you think it might be a bad capacitor? Voltages are ok, right?

Voltages seem fine as far as I know. Could be a capacitor but I don't really know how to test them other than through substitution. Anyone got any tips on how to check capacitors?

Bulatovic wrote:Try rewiring pots... aaaa... just think of these things that you can check easily...

I will try shorting out the pots one at a time and see what I find.

Conger,

Take a listen to my 5E3 (goto my Soundclick link below and listen to "The Killer"). Does your 5E3 break up like mine? Can you record your amp?

Darryl

are you sure all your resistors are the correct values? I've accidentally used a 4.7k instead of a 470k before

Can't exactly say why, but I'd be looking first at input jack wiring...someone suggested leaving only one in-circuit and that is a great idea. If that fails, I'd be looking at the grounding on the output jack.

With voltages looking good, I guess I'd be looking at the bookends, not the stuff in between.

My guess is that you have an improper ground hiding in plain sight.

Darryl wrote:Take a listen to my 5E3 (goto my Soundclick link below and listen to "The Killer"). Does your 5E3 break up like mine? Can you record your amp?

My 5E3 breaks up nothing near that whatsoever even if I set it to 12 and slam the guitar.

I don't believe that I have the wrong expectation of what a 5E3 should sound like, and have been checking out 5E3 sound clips over the last 6 months or so. There is just no real gain in this amp to speak of.

Great track by the way.

Phil_S wrote:Can't exactly say why, but I'd be looking first at input jack wiring...someone suggested leaving only one in-circuit and that is a great idea. If that fails, I'd be looking at the grounding on the output jack.

With voltages looking good, I guess I'd be looking at the bookends, not the stuff in between.

My guess is that you have an improper ground hiding in plain sight.

I have already un-soldered all jack connections and used a single cliff socket straight into the first 68K input resistor, and grounded at the input jack. Also tried grounding at other places. No change.

I have also redone the grounds which all trace and measure out OK.

teletroy wrote:are you sure all your resistors are the correct values? I've accidentally used a 4.7k instead of a 470k before

I have checked and checked and they are all OK, but I know how easy it is to "see" what you want to measure. I am going to re-measure all resistors using 2 different meters today, ignore the value on the layout, write down the measured resistance and then check all recorded resistances with what's on the layout and schematic.

I have traced out the schematic using my board as the source and all resistor values and connections check out fine. I was measuring resistance from adjacent components or links to the pins in the tube with the tube half pulled out to expose the pins.

The only thing I found which was out of spec was one of the volume pots read 835K instead of 1M. I changed it for a 1M pot that measured 1M.

I am now 100% sure that the circuit is correct and if there is a piece of stray solder or wire under the board, I can't detect it by measuring between adjacent components. I have even tried to blow out anything lose under the board with strong blasts of air.

One thing I did notice, is I left off the 4700pF tone cap connection to ground and the gain increased a bit. I always thought that the 5E3 tone stack was pretty efficient so I don't know if this is normal or maybe a pointer to the problem.

Now if I use a 12AX7 in V1 when the volume is on 12 I get more breakup than before but still way less that my 5F2-A. This is driving me crazy and using up valuable time that I should be using playing through the amp.

I have now removed the board, removed solder and re-soldered board and rewired jacks and pots, roughed up the bloody brass plate and chassis underneath it and rebuilt it. The symptoms remains the same.

I have been tracing the signal through the circuit. I found a guitar tuner output to be too low so I used an iPod looping a 440Hz sine wave. All 4 inputs give the same reading. All voltages are referenced to ground.

Here's what I get.

The voltage on pin V1 7 (12AY7) is 0.006VAC.

Just after the first coupling (0.1uF) cap and going to the volume pot, I get 0.127VAC on low volume and 0.193VAC on Max volume for that channel. This value decreases with the volume control and I can also see it decrease if I set the volume to 12 and then adjust the other channel volume to full.

I can't read the voltages on 1 or 7 because it jumps about too much.
I get just a few mA of DC after each coupling cap.

The voltage going into is V3 (pin5) is 0.955VAC and V4 (pin5) is 4.37VAC on the low volume setting and 10.8VAC on max volume. The other 6V6 is slightly higher with 4.51VAC and 11.3VAC. I can't get the DVM to read the output voltages.

Do these voltages look OK? Is the difference in voltage between V3 and V4 acceptable?

I've still got no gain!

I pulled a marked up schematic someone sent me when I was building my 5E3. I think that your B+ rail voltages are all too low.

According to that schematic, output from the rectifier should be around 410V. B+ supply should be roughly 410vdc, 365vdc, and 255vdc.

I have another schematic showing 391, 339, and 242.

I'm wondering if your voltages are too low to wake up the amp? They aren't all that low, just about 10-15%.

I'm sure you recognize this, but thought I'd mention that the two volume controls on the 5E3 are interactive. It helps to have both of them above the "0" setting.

I see you have not posted an email address. If you send me email at psymonds at comcast dot net, I will send you those two schematics I've got. I found them very helpful when trouble shooting my 5E3 build.

Phil_S wrote:I see you have not posted an email address. If you send me email at psymonds at comcast dot net, I will send you those two schematics I've got. I found them very helpful when trouble shooting my 5E3 build.

Thanks Phil. I've just sent you an email.

The voltages I get are in line with Bruce Collins Mission 5E3 schematic which gives 370-3535V, 305-320V and 215-235V. These are supposed to be the 110V correct wall supply voltages for a vintage 5E3.

I'm a bit concerned that the input voltage seems to be low. I'm going to investigate it further when I get some time.

EDIT I just check my DVM spec (http://www.uni-trend.com/UT60A.html) and the minimum AC voltage range is listed as 4V. I'm wondering if this meter is not sensitive enough and if I should get a more sensitive meter.

Episode 43 of the Search for the elusive 5E3 gain monster.

Today, I moved the 100R filament resistors off the V4 socket that were tied to the cathode, and tied them to ground instead. Also I ran a ground directly to the speaker socket. Unfortunately the amp is just the same - still low on gain. The amp is just as quiet with the 100R filament resistors grounded so I will leave them that way as the V4 socket was getting too crowded.

One other thing I have noticed is that what little gain there is, appears to be at its maximum when the tone control is maxed. Is this normal behavior for a 5E3?

One other thing I have noticed is that what little gain there is, appears to be at its maximum when the tone control is maxed. Is this normal behavior for a 5E3?

That's the way mine works.

Something I've noticed with the 5E3 - it is kind of unique in the character of its gain response, you can play softly with the amp cranked and you will get a very nice clean sound at somewhat listenable, polite volumes, then if you dig in with the pick and play a good hearty power chord, the amp will put out fairly heavy Neil Youngish distortion. It's very touch-responsive in that you can get the kind of variation just through picking technique that you would normally need to adjust your volume control for in other amps.
I imagine if you had an old Fender with relatively weak pickups set up low so that there is some distance from the strings, you might have a hard time getting any distortion at all out of it.

At least that's the way my clone works, maybe mine is defective somewhere too but I just assumed that's the character of the amp, the cathodyne pi doesn't drive the output tubes that hard, so you don't get that extra 50% over the rated clean power you get with outher amps that have a LTP.

Hope that helps and that it was disinformation-free!

Whilst it may not be the source of your problem I think there is something a little strange with the PT arrangement. The spec for the PT on the Mission site gives a value of 122V for the primary (in line with current US wall voltage) and if a similar wind is used to series with the first it would suit a wall voltage of 244V, whereas here in the UK we have a 230V supply (just a thing the EU did to be kind to old tube amps) This should make the secondary voltages somewhat lower than spec?

Mission also state that they supply genuine NOS 5Y3's, which have a fair voltage drop. Have you thought of using a GZ34, a Sovtek '5Y3' (I'm a tad worried by those) or perhaps diodes to get the voltage up?

If higher voltage dosen't do the trick I guess it's a question of checking other areas which would affect gain. Have you tried subbing the bypass cap on V1a,b and the one on V2 (P3)? They're fairly low voltage (63V) and on V1 you could try anything you have on hand from 0.68- 25uF and on V2 2-25uF (just to see if you have a bad cap and you can put in the 'correct' value later)

Alexo wrote:

Hope that helps and that it was disinformation-free!

All information is good. You make a good point but I'm sure there is a lot of gain missing here. Even with a 12AX7 in V1 and trying 3 different guitars being played hard, I still don't get anything near Neil Young. This amp is a crunch free zone.

Strat wrote:If higher voltage dosen't do the trick I guess it's a question of checking other areas which would affect gain. Have you tried subbing the bypass cap on V1a,b and the one on V2 (P3)? They're fairly low voltage (63V) and on V1 you could try anything you have on hand from 0.68- 25uF and on V2 2-25uF (just to see if you have a bad cap and you can put in the 'correct' value later)

The voltages I get are all in line with the Mission values, i.e. 355v-370v, 305v-320v and 215v-235v on the 3 filter caps. These are supposed to be the 110V wall correct vintage voltages for a 5E3.
I haven't tried another cathode cap on V1. I will try it and report back.

With a new more accurate meter and my iPod output turned up to a more healthy ~50mV output level, playing the same 440Hz sine wave, here are the voltage readings I get.

Bright Channel, Hi input voltage at 68K resistor junction = 52mVAC
Bright Channel, Lo input voltage at 68K resistor junction = 35mVAC
Normal Channel, Hi input voltage at 68K resistor junction = 52mVAC
Normal Channel, Lo input voltage at 68K resistor junction = 35mVAC

Then using the same signal in the Bright Channel Hi input:

The voltage on pin V1 7 (12AY7) is also 52mVAC.

Just after the first coupling (0.1uF) cap and going to the volume pot, I get 1.27VAC on full volume, tone set to max. This value decreases when the Bright volume control is turned down and I can also see it decrease if I set the volume to 12 and then adjust the other channel volume to full. This voltage also decreases a bit as the tone control is turned down from Max.

So this is an amplification of about 24X. Is this the right sort of amount of amplification for a 12AY7?
As an experiment, I changed the 12AY7 for a 12AX7 and the max voltage at the same point was 2.5VAC which equates to an amplification of about 48X. I then changed back to the 12AY7.

I get just a few mA of DC after each coupling cap.

The voltage going into is V3 (pin5) is 27.2VAC and V4 (pin5) is 28.9VAC on max volume. These readings reduce as the volume control is reduced.

So how do these voltages look? Where's my gain going?

One thing I did notice is that when I am measuring the input voltage where the two 68K resistors come together, the voltage increases from 52mV to about 62mV when the volume control goes from about 10 to 12. Could this be extra signal being picked by the hum induced by the probe touching the input and then amplified by the circuit?