Volume

[davidwpack]

My last build (KT66 amp in another thread) sounds great but is only half the volume of an identical amp that I built before this one. Unless I'm repeatedly overlooking something all the component values are identical. I've got a couple weird readings  on the 1 ohm resistor in the newest amp that resolved somewhat when I switched V4 and V5 around but not completely. I thought perhaps some weak tubes so I completely switched tubes between  the loud amp and the not-so-loud amp with no change. There's also a voltage difference  in V3's cathodes between the 2 amps. I'll post pictures of the voltages in the 2 amps. If they're not legible I'll type out the voltages. I'm not sure where to go from here. Like I said the amp sounds good but the volume difference rally bugs me. Anyways, if anything stands out PLEASE let me know!?! I'm doing most of this from a phone so hopefully the pics show up. The first one is the new, not so loud amp.

[davidwpack]

The loud amp.

[davidwpack]

Oh and schematic.

[nandrewjackson]

How identical are the 2 amps? Same brand/model transformers? Same brand/ratings resistors and capacitors?

[shooter]

too add to the list;
same speaker, same guitar n cable, same speaker cab?

a scope will be your VERY best friend for this, even a buddy with one, or pay a tech for 15minutes of time

[davidwpack]

Same values of everything. Same speaker cab. Only difference is that I used a 1k bias range resistor for the first one and had to use an 8k for this one. Also it's a Classic Tone OT in the new one with 4,8, and 16 ohms out and the loud one has a generic 2,4, and 8 out. I just replaced some coupling caps that I suspect was shitty quality. Getting ready to power up and recheck now.

[davidwpack]

Everything put back together. The tone still sounds great but I STILL only have maybe 1/3 of the volume of the other one. I've got one of those cheap scopes that Sluckey posted in the tools area of the forum. However, I've never used one and I'll have to figure it out. I can try to figure how to scope it Tuesday morning when I get home from work. One more thing that's different is that I have a push/pull bright switch on this new amp. The loud amp just has a permanent bright cap. Could be losing signal there maybe?  Anything else stand out that I can check out before Tuesday? Thanks.

[shooter]

If you have them both, before Tuesday, AND you're bored;
pull all the tubes and ohm all the socket pins to either ground or B+ based on "where the pin heads, ohm all the pots wiper to 1 end turning 0 - 10.  In a side by side, something should POP out.  If not 4 quick checks on my cheatsheet on both and you'll find something.  Make SURE to set all the pots the same on both, AND leave the switch engaged like the other one

[davidwpack]

Those mVAC points to chassis ground are: New amp: 1=298 VAC 2=243VAC 3=0 4=0.
Loud amp: 1=315VAC 2=260VAC 3=0 4=0.
The meter I'm using doesn't have a mVAC range. I've got a new Fluke on order that's also supposed to be here Monday or Tuesday.  I don't think the meter is reading AC correctly. 315 VAC? But yeah I work 24 hour shifts that's why it'll be Tuesday before I can start scoping.

[shooter]

sorry, you misunderstood, those are scope points, you inject a 50mVAC into the amp and look for the signal on the scope at the 4 points

[davidwpack]

Ohhhhhh. Ok Cool. I'll already have a head start for Tuesday morning then. I also considered that the OT was mislabled...or off spec....or..I don't know. I'm determined it's nothing too complicated.  But yeah thanks Shooter! I'll get on that as soon as I get home.

[shooter]

I work 24 hour shifts

understand, the last 24 yr job was basically 24/7-365 on call, paid well but then it n I got old 

[davidwpack]

Yep. This job was old 15 years ago. I get a few 15 or 30 minute naps here and there. Sleep deprivation has disrupted my circadian rhythm for so long that that's how I sleep when I get home too. Pay's pretty decent but I burnt out a long time ago.

[shooter]

Sleep deprivation has disrupted my circadian rhythm

mine has been messed up since birth    probably why I was pretty good at my job til I burnt out
when you no longer have a boss, smoking a twisty helps with the burn-out  and the rhythms 

[davidwpack]

Ha yeah. That's the only thing that's kept me doing this for so long. I tried to quit once...and I was miserable for 2 days. Haha.

[Tony Bones]

What happened to the the voltage on the cathodes of the PI tube when you swapped between amps? Did the difference stay with the amp or follow the tube?

Also, be sure that you're using the same tap on both OT's. If one is 8 ohm and the other is 16 it could account for a large difference in output, partly due to the difference in load and partly due to the difference in NFB.

[davidwpack]

I'm at work right now or I'd give you exact numbers but the voltage on the cathodes DID come up and I  believe it was 38 or 39vdc.
Yeah, I ran 4 ohms out into a 4 ohm load on both amps. Thanks..

[davidwpack]

Yeah the voltage on the V3 cathode came up from 35.2 to 39.7v. Anyways I'm home and just got set up with the amp, scope, and signal generator. Don't have a clue what I'm doing but I'll try the 4-point check if I can figure it out.

[davidwpack]

Ok, here's what I'm working with. Still have no clues...or owner manuals to speak of. I'm not even seeing voltage on the generator.

[shooter]

fumble through the scope menus, you want;
AC coupled
a timebase of ~~ 1milliSecond (Freq = 1/period time) so 1/.001 =  1Khz
voltage scale ~~ 500milliVolts to start

your siggen;
Sine wave
1Khz
continuous
start with 500millivolts

once your scope can "see" your siggen;
drop the siggen to 100mV sinwave

that should get you a "ballpark" sidebyside of the 2 amps
EDIT
by injecting the sigen into the input and measuring the 4 points I pointed out

[davidwpack]

Looks like 5mV is as low as the scope goes.

[shooter]

voltage scale ~~ 500milliVolts to start

[davidwpack]

Godddd! 30 hours and no sleep=dyslexic dummy. Sorry. I'm slowly getting it.

[davidwpack]

Ok. Freq= 1KHz, Amplitude=.5 V. Should I adjust OFFS, DUTY, or PHAS? Also I've got the positive SigGen lead clipped on the positive on the input jack. Should the negative clip on the chassis ground? Sorry for dumb questions. Anyways with that I'm just seeing flat sqiggly line on point 1.

[sluckey]

Connect the sig-gen directly to the scope with a BNC cable. Don't even connect it to the amp until you can see the signal on your scope.

[davidwpack]

I had to take the "clip tip" off the probe. That's why I was getting nothing. This is what it's showing now with .5 or 5oo mV and at 1V. Is this what I should be seeing?
Edit: all 4 points

[shooter]

close but NO cigar
should be a sinewave, you're missing the neg side, re-check the siggen.  plus, each scope "graph" square should be 500milliVolts vertical, AND (I think) 1Khz horizontal (might be 1khz full screen) so either 1 sine per square, or 1 sine per screen

[davidwpack]

Here's another couple questions: I'm not using this cable in the picture. Should I be and could it be why there's not negative? I don't know where it attaches if so???

[davidwpack]

Nevermind...I think. I attached it but now I'm not getting readings again.

[shooter]

Like Sluckey said; bnc scope to sigen, if you don't have a bnc, NEXT order, pick one up.  that said, you need a signal AND a ground connection between both.  That cable you show is the scope ground, it needs to go back on the scope then to the outer shell of the bnc on the siggen, the tip of scope lead needs to go into the small female of the sigen.  BE careful because with the "cap" off the scope probe, that metal "band" is a ground and can touch things it shouldn't.  IF I have to do it like you are I find a small solid wire that fits snug into each female pin, the I gator clip the outter shells, no probe required. BUT it can get or be pretty noisey

[davidwpack]

I hooked them up directly with the BNC cable and got perfect little sine waves. Then I hooked the postive and negative of the SigGen up to the + and - of an instrument jack. I hooked the positive of the scope up to V1-2 and then V1-7 and the negative to ground on the terminal strip and still get the same sine waves. Scoping past that on point 1 and beyond I'm getting nothing.

[davidwpack]

Well I got far enough to read sine waves on V1.   These tube sockets are not the best I've used. I'll get back on this Thursday. I've got another 24 hour shift starting early in the morning. Thanks Shooter and Sluckey for helping me to figure out how to hook up the Generator and scope!!!

[sluckey]

If you're gonna mess with sig-gens, scopes, and guitar amps, you need several 6 foot RG-58 BNC cables. And a bucketful of adapters. Here's the first adapter to buy. You could use it right now to connect the sig-gen directly to the amp input jack...

https://www.amazon.com/Pomona-1297-Adapter-Phono-Plug/dp/B06Y1HDSCS/ref=pd_cp_23_1?pd_rd_w=WS3lh&pf_rd_p=ef4dc990-a9ca-4945-ae0b-f8d549198ed6&pf_rd_r=RPGTNM1XM8E1D9H568ST&pd_rd_r=4b003876-7c0f-11e9-825e-f767610a7f33&pd_rd_wg=9QINT&pd_rd_i=B06Y1HDSCS&psc=1&refRID=RPGTNM1XM8E1D9H568ST

[davidwpack]

Yes! I wondered if they made something like that. I ordered 3. Thanks!

[ALBATROS1234]

if all else fails, i know its incovienient but swap the output transformers. if the volume loss moves you got your answer.

[davidwpack]

Ey. I think I've narrowed it down. Just wanted to post this. I had to decrease the voltage on the SigGen to begin with. The images are in order. Here's the voltages I had to use for the readings. I had to decrease even further for point 2. Anyways...
Point 1= @ .1 VAC
Point 2= @ .05
Point 3= @ .5
Point 4= @ .5
I'll poke around some more and try to narrow it down. Here's pics...in order.

[davidwpack]

More

[shooter]

is only half the volume of an identical amp

do you have the "original" to compare?

there should be a knob/menu to adjust the trace so it's centered on the screen, comes in handy when you're looking at symmetry in the sinewave.

I typically set all gain/vol to max, and all tone to 5, can be annoying if it's into a speaker instead of a dummy load 

I would expect TP2 to be => TP1 

[davidwpack]

Point 2 is at half the voltage of point 1. Point 1 is .1 VAC and point 2 is .05VAC. Yeah I'm going to compare to the original here in a few. There is an adjust knob for adjustments. I'll see if it centers too. I think the signal gets mucked up in the tone stack.
Edit: The signal generator is turned down by half at point 2.

[davidwpack]

I've got a big drop at the top of the 1st .022 cap in the tone stack. I'll get the other amp out and compare. I need a second amp cradle.

[shooter]

I've got a big drop at the top of the 1st .022 cap in the tone stack

things get wonky inside a TS, TP2 is kinda/sorta before the TS and TP3 is after.

the DCCF should be a pretty good bump up from .1vac, the 1st half is gain and the 2nd half is sorta unity but from my experience it's about 10% loss from the gain of the 1st half

[davidwpack]

Tp2 has a huge bump from 1. Tp3 has a big decrease. Tp4 looks pretty much exactly like Tp3. So something's not right between Tp2 and Tp4. Should I start bypassing stuff with alligator clips or...? So basically Tp2 has way more signal than 3 and 4. I'm confused.

[ALBATROS1234]

somehow signal is being shunted to ground?

[shooter]

Tp3 has a big decrease

that is basically normal, a TS will eat a lot of signal
TP 3/4 being = is probably ok, but a sidebyside will tell, 4 will be a huge "loss" in voltage because at that point we want current, so the OT steps done volts while stepping up current to drive the speaker

[davidwpack]

Yeah side by side there's a huge difference between point 4 on both amps. I'm getting strange readings on a couple of pots too but I didn't compare pot readings between the 2 amps yet. But...again I'm out of time but after this 24 hour shift I'll start a 3-day break. I'll be back at it Saturday morning. I wish I could lug all this stuff to work easily. Thanks for the replies guys!!!

[shooter]

strange readings on a couple of pots

reading ohms with a meter, or signal with your scope?
I would touch up the lugs with a solder re-flow, especially the grounds
are both TP 3 "close" with signal ?

having a sidebyside, you should be able to walk it in pretty quick, AFTER lots of sleep and a good meal!  no sleep and highvolts are never good together, trust me on that!

[davidwpack]

I was reading them with a meter (wanted to try my new Fluke out).  Yeah I'm pretty sure both point 3's were relatively close. You're right about the sleep. I quit while I was ahead. I imagine this must be close to what it's like to get Alzheimer's. I scare myself sometimes.

[shooter]

both point 3's were relatively close

that makes it A "PA" problem, pi, power tubes, OT n speaker circuit.

spend quality time with your fluke doing pin for pin ohm checks on each amp.  Betting while you were sleep walking you replaced a 100 ohm R with a 10k 

[davidwpack]

That's what I'm thinking too.  Getting closer I guess.

[shooter]

this probably should been asked 45 posts ago, 
did you try the anemic with NFB disconnected?