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Hi... my first post and my first 18 Watt build

I have a problem that there is no sound unless you crank the 2nd volume to max, and the input sound can be heard ( very very faint) .. along with some buzzing. If you crank the gain to max it will go quiet. On the RH channel, the sound cannot be heard. It's the same for both the 6V6 and the EL84 tubes... I also get no sound when I switch the POWER boost switch, but I can see the voltage change on tube V2, when switched.

I checked all my voltages, retraced every connection, component values and Cap orientation and checked al the connections for continuity.

The only problem I found was that resistor R11, which is part of the tone/volume circuit is a 470 K instead of a 47 K (oops on the color banding identity) I don't have the correct resistor, so I can't change it...

I wonder if that could cause the problem.

I am also not totally clear on the input jack coax wiring, so that may be wrong? It sounds like a crossed wire to me..

advice?

Which channel is not working?
Post all the voltages & compare them to the layout and see if there is any big differences?
If all the voltages are right, then carefully touch the grid of the premap tube with a conductive small screwdriver and see if you get a pop. Grids are pins 2 & 7 on the 12AX7 and 2 on the EL84 and 5 on the 6V6.

Check that the tube selector switch is wired correctly as well.

470K in the tone circuit would take most of the bass out (below 1K)and it would make the tone sound pretty odd.
Was the 47K resistor missing? You can sub 56K - 33K carbon film.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

The channel that (barely) works is the LH channel no response at all from the RH
yes the 47 K resistor was missing

the voltages are below:

V1 - 12AX7
--------------
Pin Volts
1 134
3 .8
6 132
8 .8

V2 - 12AX7
--------------
Pin Volts
1 230
3 2.03
6 230
8 1 229

V3 (PI) - 12AX7
--------------
Pin Volts
1 161
2 40
3 62
6 182
7 46
8 62

V4 - EL84
-----------
Pin Volts
3 18
7 284
9 215

V5 - EL84
-----------
Pin Volts
3 44
7 284
9 214

when I touch the pins on the tubes they pop a little bit a lot on pin 7 of V3

as far as i can see the selector switch is wired correctly.. it pops when you switch

does it matter if I have one ecc83S ( from JJ) in the preamp?

Success!!!!

I had missed connecting the wire from the RH tone control to the turret board. I was concentrating on the tube side of the amp ...

It sounds good!!.. The 6V6 are a LOT quieter than the EL 84's.

The LH channel still doesn't work, but know I know the pre-amp works I can concentrate on that side..

Something may still be wrong. Recheck the voltages as they were/ are out of whack.

>>> Specially Pin 3 on the EL84s is way out. It sohuld be 12V. Check your bias resistor value. The B + is too low as well, is should be around 340.


Get these sorted out.

If you have a VRM, make sure it is at max for these readings.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Good news but check the voltages again. The v6 are quieter, but I wouldnt say a lot, about 3 db. There is a tweak for these if you want to drive them harder. But get it all going first.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

B+ is 344

The VRU works well and at full volume it only seems to rob 2 or 3 volts or so..

here are the rest of the voltages:

V1 - 12AX7
--------------
Pin Volts
1 136
3 .88
6 138
8 .9

V2 - 12AX7
--------------
Pin Volts
1 184
3 1.69 no boost , boost on 2.04
6 244
8 242

V3 (PI) - 12AX7
--------------
Pin Volts
1 185
2 47 ( big time snap when i use the meter)
3 72
6 196
7 50 (goes silentwhen I use the meter)
8 72

V4 - EL84
-----------
Pin Volts
3 12
7 338
9 325

V5 - EL84
-----------
Pin Volts
3 11.77
7 332
9 320

That's better. Check the power supply chain to V1, the voltages seem a little low, especially the cathodes:

V1 - 12AX7
--------------
Pin Volts
3 .88
8 .9

The VRM is working according to design too. I'll send out a 47K resistor.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

the wire from pin 3 and 9 are short and terminate in the turret board.. no problems with the wire.

I am now at a loss...


ther is 6.0 vac on pins 4 5 to 9

What is your mains voltage? The heaters voltages should be closer to 6.3VAC.
It's just that ideally you want the cathodes there to be closer to 1V. Obviously it works.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

The mains voltage is 114 VAC.

I did go to another plug that the incoming was 113 volts, and the 6 volt to the tubes was 5.9. I can't believe the transformer is so sensitive.


Well.. I knocked the EZ81 tube and broke the Glass nipple from the end, so it is no longer a vacuum tube...

I guess I need to wait until a new one arrives.

I guess I will resume trouble shooting this amp then...

O.K. several weeks later, I finally got back to this beast.
Well it turns out resistor R8 was 1k instead of 100K .. ( on the gain pot, input to pin 7 of V2) I must be getting color blind as I age.. I changed it out for a 100K Takman brand (nice pink color) resistor.

It doesn't really make sense to me that a 1 K resistor would cause this problem?

I first tried the amp with no resistor (maximum gain) but it was too much.

I also noted that this TMB channel is not as loud as the sIII channel..

I played it for a while through my Warehouse 1 X 12" Green Beret speaker. Sounds O.K., but I think I need to tune the sound.



thanks


Marty

Marty, It's math: 6/120V = 5% voltage reduction over spec. So all the AC will be 5% less so 6.3 V X .95= 5.985V

R8 dumps the gain a bit. 1K would be more gain, 100K less.

How do you want "to tune the sound."

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Well I played this amp for several hours tonight, and I'm not sure I need to do anything yet to change the 'sound'. I do notice that the sIII channel is about 1/4 the volume as the 'normal' channel.. when you chain them together the sound is great . Lots of flexibilty. I like the 6v6/EL87 switch It really changes the character.

here are some pics of the finished amp.. I did the head cabinet as my take on a 'modern' Marshall 18 Watt.. You can see through the cabinet grill and see the tubes, as per the new Marshall head cabinets, but the size of the cabinet is the 'small' cabinet size. Russian birch ply, Marshall elephant 'tolex', and original Marshall grill cloth from the U.K.

The speaker cabinet is the same dimensions as a Marshal 1960 1X12 cabinet and has a 1 X 12 Warehouse Green beret speaker ( supposedly like a Celestion green back).

I added the VRU on the front panel in place of the standby switch, called it level, and added a 3 position off/on/on toggle, for standby (idle) and on. I had a new faceplate made by MOJOTONE. I also used a square 'Marshall like' power indicator, and a Marshall power switch bezel. Interestingly they are almost the same as the MG toggle switch bezels. I guess it's a 60's British thing.

Looks good. The two channels should be very close to the same volume level. So there's is still something not going on there.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I thought something wasn't right.. When I back the gain to 5 or so it is really really quiet, even with the volume at max on that channel. The mid pot seems to really affect the volume aswell..
Any thoughts?+

You have to go back to the components, including the pots and check including the wiring. Tubes , voltages etc.

_________________
Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps