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Hi
Just finished my 18 sIII
I changed the bias kathode R with ground and provided -10-13V at R18 and 19. Further no sic.
Basicaly it amplifies, it's working! But there is a humm I cant get rit of.
There is a very light one which is not so anoying but cracking up makes it very bad.
I was checking the voltages and noticed that V3-2 is 0.
My B+ is also lower than I wanted 300V. I measured the ripple on B+ and that gave me 115mV so that is not to bad I think.
Any way I am going to check the voltages again to night.
So far not to unhappy...just to let you know.
After the measurements I will post the list
Ciao
Ed

Oke, these are my measurements (I must remember to isolate the the lead connections to the DVM next time

B+ with tubes 300V
B+ without tubes is 396

V1 - ECC83
--------------
Pin Volts
1 120
3 0.8
6 119
8 0.8

V2 - ECC83
--------------
Pin Volts
1 139
3 1.3
6 219
8 138

V3 - ECC83
--------------
Pin Volts
1 176
2 47
3 68
6 174
7 47
8 68

V4 - EL84
-----------
Pin Volts
3 9.6
7 291
9 279

V5 - EL84
-----------
Pin Volts
3 9.4
7 291
9 281

As the values are overall somewhat lower I take it I will not reach the full 18 watts. This is no big deal for me however.
The El84's are not mached, together with the ECC83 they come from the bottem of my junkbox.
Please let me know any comment.

Ed, are you able to get some pictures of the guts uploaded? Then we have a chance of helping you.
Nigel

Nigel
Great, yes I will try to do so but my daughter has my complete multimedia eqpt as she got this baby a month ago
Anyway the design is pretty much the same as the original sIII.

Just to see where the hum came from I grounded the cap's at the inputgrids of the EL84, almost no hum, so far so good.
My trannies come from anchient radio gear by PHILIPS.
Well I got to go will get back to night.
Ed

Yes a picture of the general layout is good. What grounding scheme did you use? Was it the same as the layout here?

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

Yes a picture of the general layout is good. What grounding scheme did you use? Was it the same as the layout here?

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

Yes a picture of the general layout is good. What grounding scheme did you use? Was it the same as the layout here?

http://www.trinityamps.com/ForumGallery ... _v1.93.gif

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

Yes
Basicaly it's the same layout, and the same chassis shape, trannies on the same side als valves potmeters, and inputjacks are the same.
The groundings for the inputs are at the input-jacks-end. the potmeters are as needed grounded at the thick copper wire at the board.
I used shielded wire for the inputs and because they are so extremly hot also to the tone stack. (this may cost some high freqs but we ll see about tahat)
I am going to ground the input caps at the phaseshifter to see how the hum ends up.
Next I will disconnect the TMB part and only connect the other part.
I am almost shure it has to do with unpropper grounding.
My potmeters case(is this right english?) is plastic with a small metall back
see here http://www1.nl2.conrad.com/scripts/wgat ... ~cookies=1
I am affraid that they cause the humm.
Any way I did reshuffle all components so my chassis is quit a mess at the moment. I will restore it tonight.
For the pictures, I have some starting pics at 18watt.com http://www.18watt.com/modules.php?set_a ... _album.php
I hope the links will work.
Can you say anything about my voltages and the AC ripple?
As info, I built a lot of "tube things" in my life, radio's transmitters up to 1296 MHz. So I have to get this amp going or I can not meet the eyes of my friends anymore
Thanks so far anyway

Ed

Ed, here are some pictures of my scratch sIII, this has no hum at all so you may be able to compare grounding schemes.
Nigel
http://kirkby.com.au/g2/main.php?g2_itemId=487

Nigel
Looks great, is that the OT in the middle, must be, it's bigger than the PT!
The way it looks it's pretty much the same. This night I rewired the whole thing. Looks better now but the hum is still there.
It is also constant, any movement or touching does change it. Except potmeter has influence
It's the strongest in the normal channel, the tmb is much better. It has a slicht hum that one can ignore exualy the gain looks oke?
Well i quit foor to night, might have my camera back to morrow i'l put some pics this way
Thanks again sofar
Ed

Yes, my OT is pretty OTT it is a Hammond 125E clone that is overspec and potted. I think they sound great but I can't get any more, I have one left on my parts shelf.
Nigel

Oke

Found two fu***g broken pots VR1 and VR 7and a wrongly rewired heather wire. Humm is much less now but still to much. Gain looks and sounds oke.
I measured with my scope that even if I connect the 68K's at pin 7 of V1 directly to ground there is still 50 hz at the anode.
Measured the AC at the nearest 16uF cap and it was less than 10 mVolts, must be oke.
Still going strong. My cam is still with my granddaughterbaby so for now no amp guts.
Regards
Ed

I found it!

The electric system in my house, being from the 1920's has no ground contact, except for the washing maschine and dryer ofcourse.

Looking into some old guitar amp schematicis I noticed the "de-hummer" pot in the heater voltage.
A 100ohm pot was connected to the 6,3 AC Volts ant the taper was connected to earth. As I did not find a pot I connected to 50 ohms R's in series and the middle point to ground. Did this having the whole thing switched on
I thought for a moment I blew up the whole thing (idiot!) I didnt hear ANYTHING except ofcourse my guitar.
So its working great. Next step is to make the housing.
If I set, wthout the guitar, every pot to MaxCW there is a slight hiss but I have to put my ear in the speaker so no big deal.
I am HAPPY
Ed

Good stuff.

You should probably change those from 50 ohm, to 100 ohm. Put them across the 6.3 V tap, centre point to ground.

Works just fine!

Also, you may have to reverse your mains plug 180 at times if it doesnt have a ground pin on it.

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

Good stuff.

You should probably change those from 50 ohm, to 100 ohm. Put them across the 6.3 V tap, centre point to ground.

Works just fine!

Also, you may have to reverse your mains plug 180 at times if it doesnt have a ground pin on it.

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

Changed the 50 ohms to 100 oke, connected the apm chassis to the central heating plumbing, v e r y c l e a n!

Rotating my volume on the guitar, jap clone of clon strat
I noticed there is a hum peak at 50%, sound reacts as I expect however.
Is this a ground loop thing in my guitar?
Grtz
Ed

Finally got to change the pots.
Also built a wooden housing for the amp, top.
I built the Celestion G12H30 in a crate ;=(

I'm working on a website with foto's anfd progresse if any of the built so check this now and than if you like, ill post the link to night.
Regards
Ed

Oke
Things are working as they should. (All my doughters houses are oke so I have time to get back to my hobby.....)
Still working on the website.
My sIII is working great. Into the G30H12 it is so loud!
Checkout http://home.kpnplanet.nl/~gerriehorjus@kpnplanet.nl/
and see if I get my site on air.
Thanks for all the helpat this forum
GRTZ
Ed

Eddie,
Good to hear all is well with your amp. Your site came up but no content yet. Looking forward to the pictures.

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

Stephan

Put some content, photo's on the site. Changed the language into English (more or less)
Grtz
Ed