voltages on V3 (18 watt classic tremolo)

18watt-specific Tech Talk - Building, Fixing, Parts, Mods...

Moderators: CurtissRobin, colossal, zaphod_phil, Daviedawg, Graydon

Post Reply
User avatar
Bieworm
Occasional poster
Occasional poster
Posts: 457
Joined: Mon 02/10/20 8:24 am

voltages on V3 (18 watt classic tremolo)

Post by Bieworm »

hey guys

I just' can't figure out why the voltages on my tremolo tube are so off..
I just can't see anything wrong on the wiring, components,... the soldering is ok and the chopstick method gives me zero hunches.

voltages measured:

B+ after the rectifier (diode 1N4007 types + 220ohm 10W resistor) = 360V (pretty high, but no real danger?)

V1: p1 158V / p3 1.18V / p6 158V / p8 1.18V

V2: p1 223V / p2 51.3V / p3 68V : p6 225V / p7 51.2V / p8 68V

V3: p1 188V / p3 1.49V / p6 128V / p8 1.49V

V4: p3 12.96V / p7 345V / p9 340V

V5: p3 12.95V / p7 345V / p9 340V

HV1 and 2: 294V

Heaters: 2.9V both

you see that the values for V3 are pretty weird.
- I thought p1 and 6 should differ in opposite direction (p1 should be lower in voltage than p6)
--> what's the 110/150 spec value on the chart stand for? why 2 numbers? trem oscillation values?
- the cathode values are nearly 40% higher than spec'd. What could cause that?

What is the best way to lower the B+? zener diodes in the B+ line or higher cathode resistor value? (have 180 ohms in there already, plus a 2200uf/50V cap)
I also read somewhere that the 100 ohm screen resitor cap upped to 1k or higher also helps?

I really need some advice on the V3 values!!! please... ;)

the amp hisses somewhat more than normal, but my guess it's the higher B+ that's causing this..makes the amp hotter after all
0 x
"THIS should be played at high volume..preferably in a residential area"

Daviedawg
Superior Amp Tech
Superior Amp Tech
Posts: 612
Joined: Fri 01/08/10 2:00 am
Location: Scotland

Re: voltages on V3 (18 watt classic tremolo)

Post by Daviedawg »

V1, 2 and 3 are not a serious concern, or any concern really. A little high as you know and consistent throughout. V3 relationship of the two triodes depends how you wire it. Mine look like yours.
Your cathode voltages on the EL84s are too high for the best performance. But if you are intending to lower the overall voltage then wait until after you do that to make any cathode resistor adjustments. Aim for 11.5 to 12v
I used zeners to lower my DC voltage. Working a few values until I got my target. I think I have two in the circuit but it was ten years ago and no recent visits have been made to the guts. for me they give a more consistent predictable outcome.

Dd
0 x

User avatar
Bieworm
Occasional poster
Occasional poster
Posts: 457
Joined: Mon 02/10/20 8:24 am

Re: voltages on V3 (18 watt classic tremolo)

Post by Bieworm »

Changed the resistor after the diodes in the rectification from R120-10W to R220-10W.
Cathode resistor = R180-10W
Cathode cap = 1000uf/63V
Screen resistor changed from R100 to 3.3k

This seems to be the best combination for now (gonna try a R150 cathode resistor when I get one)...I tried the 220R cath. res. and the voltage went over 13.5V. Also tried the 120R and voltage went to 10.5V, which is too low and the amp sounded dull. So for now the 180R is best, but still have a little over 12V. Me thinks it's a stayer like that:)

Here's the chart:
15835877471738966981842329023939.jpg
You do not have the required permissions to view the files attached to this post.
0 x
"THIS should be played at high volume..preferably in a residential area"

bvayling
Occasional poster
Occasional poster
Posts: 120
Joined: Sat 03/30/13 12:53 am

Re: voltages on V3 (18 watt classic tremolo)

Post by bvayling »

I think I have similar issues on my build, also a traditional trem combo. Josh said the B+ is too high on my amp (360V), now that the plate dissipation is within range. I’ll have to look into the methods of lowering it.
0 x

User avatar
Bieworm
Occasional poster
Occasional poster
Posts: 457
Joined: Mon 02/10/20 8:24 am

Re: voltages on V3 (18 watt classic tremolo)

Post by Bieworm »

bvayling wrote:
Sat 04/04/20 10:17 am
I think I have similar issues on my build, also a traditional trem combo. Josh said the B+ is too high on my amp (360V), now that the plate dissipation is within range. I’ll have to look into the methods of lowering it.
My classic 18 watt has 348V and my TMB tremolo has 361V. I like 'em both the way they are. The ideal voltage is 340V, but that's not per ce what you have to follow. If it sounds good to you it's perfectly all right..and safe too, if that's what you fear. A high B+ can give you also higher clean headroom. I like that on my classic, because I am afraid otherwise it will be on the edge of enough for a band situation. I'm used to a vibro king, so I like the idea of having some spare headroom. The classic will be my plan B in case the TMB tremolo won't cut it.
These are my action readings on the classic:
15860264701623754365775706107825.jpg
You do not have the required permissions to view the files attached to this post.
0 x
"THIS should be played at high volume..preferably in a residential area"

bvayling
Occasional poster
Occasional poster
Posts: 120
Joined: Sat 03/30/13 12:53 am

Re: voltages on V3 (18 watt classic tremolo)

Post by bvayling »

I hear you, Josh did mention that 345V B+ was for the "classic" sound. I'll play it like this while I wait for the zeners and decide.

I often find myself on the edge in certain band situations with these amps. One of the drummers I play with hits pretty hard.

Here's the one I've played the most. I haven't taken the new one out yet. It's a LiteIIB from an AO35 Hammond reverb unit. I call it the Gammatron. After what I'm learning here I might have to back into it and check all the voltages, it has some issues. It breaks up pretty quick!
IMG_0672.JPG
You do not have the required permissions to view the files attached to this post.
0 x

User avatar
Bieworm
Occasional poster
Occasional poster
Posts: 457
Joined: Mon 02/10/20 8:24 am

Re: voltages on V3 (18 watt classic tremolo)

Post by Bieworm »

bvayling wrote:
Sat 04/04/20 3:04 pm
I hear you, Josh did mention that 345V B+ was for the "classic" sound. I'll play it like this while I wait for the zeners and decide.

I often find myself on the edge in certain band situations with these amps. One of the drummers I play with hits pretty hard.

Here's the one I've played the most. I haven't taken the new one out yet. It's a LiteIIB from an AO35 Hammond reverb unit. I call it the Gammatron. After what I'm learning here I might have to back into it and check all the voltages, it has some issues. It breaks up pretty quick!
IMG_0672.JPG
I don't know what or how, but my classic hardly breaks up unless I really dime it. I like it like that. It responds to my push pedal really well to drive it some.. so.. ok here. The TMB tremolo breaks up immediately. I hot that a little better with some resistor adjustments. But it needs some more clean...
1 x
"THIS should be played at high volume..preferably in a residential area"

User avatar
JMPGuitars
Super Duper Admin
Super Duper Admin
Posts: 1981
Joined: Tue 09/18/12 8:00 pm
Location: South Central, MA
Contact:

Re: voltages on V3 (18 watt classic tremolo)

Post by JMPGuitars »

Bieworm wrote:
Sat 04/04/20 3:21 pm
I don't know wat or how, but my classic hardly breaks up unless I really dime it. I like it like that. It responds to my push pedal really well to drive it some.. so.. ok here
The TMB tremolo breaks up immediatly. I hot that a little better with some resistor adjustments. But it needs some more clean...
Normal behavior is usually clean(ish) up until about 3 or 4, and then varying levels of dirt from there on.
0 x
'I installed a skylight in my apartment yesterday... The people who live above me are furious.' - Steven Wright
Web Design: DolceVittoria.com
Guitars / Amps / Effects: JMPGuitars.com
(anti)Social: Facebook · Instagram
Items for Sale

User avatar
colossal
Moderator
Moderator
Posts: 338
Joined: Thu 05/10/07 2:00 am
Location: In and around the lake

Re: voltages on V3 (18 watt classic tremolo)

Post by colossal »

Bieworm wrote:
Sat 04/04/20 3:21 pm
I don't know what or how, but my classic hardly breaks up unless I really dime it. I like it like that. It responds to my push pedal really well to drive it some.. so.. ok here. The TMB tremolo breaks up immediately.
Mine are the same. I have heard some amps that break up very, very early, and others not so much. I think it has to with the heat of your pickups (among other things). I have underwound and unpotted, low output PAFs in my Les Pauls so I get a fair amount of clean(ish) headroom. There is always a bit of fur on the edge of the note, but not distortion. If I open the amp up a good bit, it will snarl if I dig in. Killer amps.
1 x

User avatar
Bieworm
Occasional poster
Occasional poster
Posts: 457
Joined: Mon 02/10/20 8:24 am

Re: voltages on V3 (18 watt classic tremolo)

Post by Bieworm »

Welll.. The TMB trem stays cleaner wit a jaguar. Wit my jazzmaster it gets very furry.
With the les paul with classic 57 pups it's instant grind. With the p90 les paul it's immediatly rock

I only play the offsets 99% of the time.. where the jazzmaster takes 95% of the time
0 x
"THIS should be played at high volume..preferably in a residential area"

Post Reply