Stuck, (I can't find the issue)

[dude]

I made a copy of my Allen Old Flame amp for a friend, Amp seems to play ok but lacking in volume big time. I thought it might be something with the raw control, I put in a 100KL pot to replace the switch, it works but this problem might be in my wiring of the pot..? Pretty sure I have it correct, the old push button just shorted the tone stack to ground, the pot now shorts it slower for more control.


So the issue is low volume. I compared the two heads, my older Old Flame is much, much louder then this amp. It's a copy of a single channel Super reverb, one channel no trem. Reverb works good. It's just the low volume unless I turn the raw up, starts to ground the tone stack and amp get much louder and dirty like it's suppose too. But with the raw off, and volume and master both at 5, lacking big time over my older old flame in volume.


Here are some voltages B+447, down the rail 437, 413, 347v.                          If better pic of schematic is needed, let me know
V1, both: plates 230, grid 0, 31.8v K
V2, both: plates (reverb) 439v, grid 0, 7.7v K
V3  both: plates, 258, grid 0, 2.1K
V4  PI, one plate 251v. grid 68v, 105 K, other plate 227v, grid 64, 105 K
V5 plate 445v, screen 446v
V6 plate 446v, screen 446v
5AR4: 449v, after choke, 446v

[shooter]

Have scope might fix 

[sluckey]

31.8v on V1 cathodes ain't gonna let much if any volume through. That voltage should be about 1V to 1.5V. Suspect bad or wrong value 1.5K cathode resistors or a bad ground connection. What resistance do you measure from V1 pins 3 and 8 to chassis? Put probe on tube socket pins, other probe on chassis.

We definitely need a bigger schematic.

[dude]

I gave the wrong K voltages for V1, had 1,2,3 for each pin, said 31.8v, when it was 1.8v. Something might be wired wrong, I’ll go over the bd connections again in morning when fresh. Grounds look good on V1, l’ll check resistance tomorrow, thanks

[Leevi]

I would try to localize the issue first. Disconnect the power amp from the preamp and put a signal from another amp or source to the power amp input. I have had some cases where the problem was in the OT.


/Leevi

[dude]

I checked the V1 K's to ground, 1K5 ohms, so no issue there. I also bypassed the raw pot, and still volume is noticeably less than other Old Flame, so not the raw pot. The tone stack works well when in circuit, very well. I remember when I put the PPIMV 1M pot, I checked the three I had, used a closely match dual 1MA pot.
I traced wiring to tone stack again, looks good.  I usually populate a bd with wire hanging, go over it three or four times out of the amp, checking values and connections. Same with the chassis, PT, filaments, sockets, power supply, etc. Then install the bd. checking a few more times. No issues and amp played from the start that's when I noticed the low volume with the tone stack engaged, I played the other Old Flame, noticeable difference in vol.
This amp comes alive with the tone stack grounded out, seems like a wiring issue - if the amp plays as should with tone stack grounded out...? maybe I should look harder for wiring error. Is there any reason for decrease in volume caused by a faulty component? if so, where should I look, I checked all values before soldering...?
Leevi, the "Power Out Section" plays well  with tone stack grounded, amp roars., that seems like Power Out is working.
Is there any component that could lower volume that I should check. I replaced the first 12AX7 and PI 12AT7 with difference tubes, also the 6L6's with know good. I noticed the voltages on the 12AT7 PI tube seem high on the cathodes at 105v,: pin1, 251v, pin2, 68v, pin3, 105v other side pin 1, 227v, pin2, 64v, pin3 105. Are these voltages good? 


Don't have a scanner big enough to copy schematic best I can do:
   
.

[sluckey]

"tone stack grounded out" What does this mean. Show me on your tiny schematic.

LTP PI voltages are fine.

[dude]

"tone stack grounded out" What does this mean. Show me on your tiny schematic.

Sorry about the schematic, tap on it, will get bigger.
The pic below is the layout of the tone stack, there is a "raw button switch" between the volume and treble pot, which when pushed in, carries the ground to the mid pot, completing the signal to the tone stack, it works as it should. Button switch "out", the ground is disconnected killing the tone stack. When I said "grounded out" I meant the opposite, sorry, getting old is a drag, ha. I changed the button switch to a 100K pot so I could dial in the added gain from slowly disconnecting the tone stack (taking the ground out slowly as I turn the dial up. I have this in my older Old Flame, works well, except this time I went from a 1MA pot to a 100KA to give a better range as I never turned the 1M more than 2 or 3 on the dial.


I just soldered every joint, check all wires, all correct. Made sure tubes pins are tight. I know from my Fender Blackface days, not all amps sounded the same, some had magic, seems my older Old Flame that I built in 1998 has that magic, I don't know but the volume is a lot less on this new one, exact same amp. The new amp with volume on 3, PPIMV on 5, the volume is unplayable, too low and kind of tinny sounding. Turn the volumes to 7 and 7, louder but nowhere as loud as the older Old Flame amp, at that setting the old amp would blast you out of the room, this new one doesn't get close.
All the iron is new, from Magic Parts or Ruby Tubes, it's the same OT in both amps which both are made in USA.


Any clues would be welcomed, and hit on the photo's they will get bigger.
Thanks, al

[dude]

Maybe I have a shitty volume pot, not tapered right...? I'll check the function.

[dude]

Maybe I have a shitty volume pot, not tapered right...? I'll check the function.

Ha, might be getting somewhere, the main volume pot taper seems way off, kicks in last 1/8 inch turn, 1MA on bench has a more even taper, I'll replace it. This could be it...?

[dude]

I replaced the volume pot, much better taper swing than the old one. Now the amp has "more volume lower on the volume pot", much better swing. Old volume pot had to be on 3 to get any sound, weak at 5, then 9 or 10 all the volume came.
The new amp Old Flame doesn't sound as good as the old one and is a little less in volume but much better. Bad pot and a picky player, ha. I used a few cheap poly .1 coupling caps as I ran out of Mallory 150's, maybe that's the tone I'm missing.
Thanks for helping.