Help with mod

[chabby-ao]

I'm converting a Marshall 2210 into a 2204 and have it all hooked up.
It sounds great...just like a 2204 modded to my favorite settings.

But for the life of me I can't trace down why it's playing at such low volume.
Please feel free to give me any  ideas. Most of the components are new as far as resistors/caps and pots/power tubes go.

Of course it's with the 2210's Full wave bridge rectifier which is the only way I can use the PT and get the voltage required. But it sounds so perfect if it wasn't so damn quiet. I'll chart voltages after dinner but at first glance they looked okay except for some way high numbers on the plates of V1. The plates of the power tubes are at 457 VDC, screens slightly below that, but something major has to be wrong for it to be so quiet. It isn't even 1/ as loud as my 18 watt.

[phsyconoodler]

You wired it.Go over your preamp again and then again until you find the problem.

Did you use a hand-wired board?Any pics?

[sluckey]

Did you also keep the 2210 bias circuit? What voltage do you measure on pins 5 of each output tube? Did you just use two output tubes? Post voltage readings for all tubes.

[OldHouseScott]

And if you've got "way high" numbers on the plates of V1, make sure you don't have 82k or some such instead of 820 for the cathode resistor, or 270k for 2k7, etc.

[chabby-ao]

Yes - I hand wired it and got rid of the very weak and extremely busy PCB board it came with.

It's all post & turret now with parts I had laying around my shop.
Yes, I'm using the 2210's bias winding and that part is just fine in terms of getting the proper dissipation at the power tubes. I biased it both slightly hot and a bit cold and all points in between trying to find answers, as well as what the range would be with the bias winding and the new bias circuit I wired up using the existing pot and similar values of resistors. I'm going to change them though because it's limiting me from getting any cooler settings than 20-25% PD.

Plate voltage is at 454 VDC with Svetlanas and 445 VDC with some Mesa tubes I have laying around. The amp just sounds exactly how I wanted it to/ what I'm shooting for and has allot of balls on the Low input...wow! Not boomy or anything just deep bark. This rendition is excellent because with the low input side it's ballsy and cleaner and the high input side get's real gainy. I subbed in some non standard JCm 800 tweaks I really like off of standard, so it's right where I want it that way. And no.....I did use 820 R's at least in a couple spots.

My problem could be pre amp tube related as I have nothing here right now that is new, or been tested lately. Just allot of older tubes here right now and my tester is broken. My guess is its either that, or possibly (not in order of liklihood) input issue/grounding/leaking coupling or bypass cap/bad pot. Of course I probably need to look at changing some resistor values too because for some reason my voltage isn't dropping adequately for the preamp I don't think.

My plate voltage on v1 pin 1= 232 VDC, pin 6= 257 VDC and V2 pin 1=204 VDC and pin 6= 351 VDC and finally on V3 pin 1= 346 VDC and pin 6= 342 VDC.

Of course for simplicity sake I rounded all voltages down or as appropriate.

[sluckey]

Post voltage readings for ALL tube pins, not just plate voltages. Also, post voltages for each B+ rail node. Can you post a schematic for your exact circuit?

[chabby-ao]

I can post a link for you to look at the schematic - it's on Dreamtone amp's website and is the 2204. I stumbled upon it and liked how he had everything right there in terms of info to build it. And, like I said, I couldn't be happier with the tone. it's just not anywhere near as loud as it should be. It's baffling me big time.
I've replaced the any possible leaking caps and ohmed out the circuit/reflowed solder joints and everything is connected. Okay, I'll post all the voltages.

Here's the link (which also posts some voltages on the schematic).
http://www.dreamtone.org/pdf/NEW2204LayoutSchemBomDreamTone.pdf

[phsyconoodler]

Wiring cliff style input jacks can be confusing and so can output jacks.If you have multiple output jacks,make sure they don't have shorting bars for each impedance tap.That would very effectively lower your output power level.

[chabby-ao]

Please see voltage below all in VDC except Filaments which are in AC



V1 -
1-252.5
2 - 0.3
3- 3.10
6-254.7
7-0 with pot at 0
8-1.15 unstable

V2
1-200.1
2-1.5
3-1.18
6-344.1
7-155.5
8-201.5

V3
1-336
2-148.5
3-145.1
6-332.70
7-177.40
8-5.20

V4
2-3.425
3-434.0
4- 422
5=-35.02
6-430.0
7-3.425

V5
2-3.425
3-435.0
4-420.0
5=-35.0
6-430
7-3.425

[sluckey]

V2
1-200.1
2-1.5
3-1.18
6-344.1
7-155.5  should be only slightly less than pin 8
8-201.5

V3
1-336
2-148.5
3-145.1
6-332.70
7-177.40
8-5.20   should be the same as pin 3 voltage since it should be connected to pin 3

[chabby-ao]

Just wanted to thank everyone for suggestions and everything is working fantastic now. The problem was a combination of input wiring (I have trouble with cliff jacks and always will, I've always understood the old metal jacks better), and grounding. Coverting a 2210 is interesting because you have to be judicious on where and how you place the 3rd 50-50 cap as there's no hole for it.

I strapped one in on the V1 side of the chassis and it worked okay, but ended up buying two 47uf X 450 heavy duty radial caps and attaching them on the preamp board which shortens leads considerably having more effective ripple control and way less ground loop possibilities. I ended up grounding one to the left hand bus and the other to the right. I have the kind of buss grounds that are separated but on the board. They are pretty heavy duty copper and I make one that's attached to the start ground near the tranny along with everything at that end. Then a separate ground bus for the input side that starts where the first bus leaves off with it's own ground near the inputs. The amp is dead quiet which is why I've started using that system on every amp I've built since having so much success with it on smaller marshall type amps like the 18 watt as well as some Fenders too.

I built this one with stuff just laying around the shop and used a board I salvaged out of an organ amp and since it wasn't long enough used wood and terminal strips for the rest....hey...it works great don't laugh! I'll post a picture soon.