MB Subway Rocket Overall Volume Seems Low for 20w

[Jazz P Bass]

Those voltages are confusing me.
Those are Volts AC readings, correct?
A good input voltage would be 100mv's.
Even so, 0.1 volts at the plate of V2 implies that the tube is not working (or the circuit.)
Try sending a 100mv signal into the FX return.
That will bypass the preamp circuitry.

[chunkitup]

I had a 1k signal that a friend emailed me. I ran out of my headphone jack into the input. I have the volume as low as it will go on the computer and then measured Vac at pin2 of V2a. it measured .022Vac. I dont have a scope so I just measured the wave. I then kept the lead gain control at 2.5 and measured output of each stage. I then put the master to 10 and measured the outputs of every stage after that including the 4 ohm output. Is this not the correct way to go about this when you dont have a scope?

[Jazz P Bass]

Yeah, that will work.
Again, I do not see very much 'gain' anywhere.
Send the IK into the FX return to prove out the power amp.
It will require 100mv's, at least.
The signal at the grids of the power tubes should be in the 10's of volts to drive the output section.

[chunkitup]

Ok so I have a .09Vac input into the fx return and the pin 2 grids read 2.5Vac and 2.35Vac

And I am still hearing ringing in my ear!!!! after it has been turned off.

[Jazz P Bass]

As I said, the FX return should be 100mv's.
So your 0.09mv x 10 would equal 25Vac at the power tube grids.
The power amp is fine.
Now for the preamp.
The FX send ultimately should read 100 mv's.
So start at the first tube & the quiescent conditions: measure pin 1 & pin 3, Pin 6 & pin 8.
Work your way down all of the preamp tubes.
Those two voltages (plate & cathode) will tell you that the tube is conducting & is ready for a signal.
With a signal applied you should see a gain of roughly 30 x's the input. (Plate compared to grid)

[g1]

Does that ringing in your ears mean it was much louder than before? Just to be sure, try that .09Vac signal at the input jack. Also, try plugging a guitar into the FX return.
Between V3a and the masters is LDR2. Appears it probably mutes the signal during channel switching. LDR's seem to be a fairly common problem in Boogies. Try disconnecting the lead that connects to the 680K, in case the LDR is leaky.
Other than that, there are only 4 transistors in the EQ.

[chunkitup]

Here are the readings on the plate/cathode:
V1a 170/1.18
V1b 164/1.19
V2a 164 copper tape over the socket cant get to pin 3 or 8
V2b 165
V3a 164/1.17
V3b 132/.74

As far as the ringing in my ears. 1k really pierces the ear.

[Jazz P Bass]

DC readings look good.
See if you can boost your input signal to 100 mv's & send it through. (100 is a nice round number)
You should then see the signal at the plates in volts.
Do not forget the grid measurements of the next tube down the signal path.
That will prove out the coupling caps (Vdc & Vac).
You want to see the same Vac signal as on the previous plate & no Vdc. (if there is a lot of Vdc, the cap is leaking)

[chunkitup]

Alright I had to grab the ipod to dial in 100mv.
V2pin2 .104vac (input)
pin1 2.96vac
pin7 covered by copper tape
pin6 10vac
V1pin2 1.6vac
pin1 45.9vac
pin7 1.5vac
pin6 55.4vac
V3pin2 25.65vac
pin1 73.8vac
pin7 .042vac This is with the master on 10
pin6 2.06vac
The power for the 4 transistors (contour circuit)should be -30v as stated on the scheme but I am only getting -15v

[Jazz P Bass]

See post #21.
Disconnect the LDR at the MV circuit.
I don't know what would pull down the -30V supply.
(By the way, that diode in the schematic for the -30 v is drawn backwards.)

[chunkitup]

The vactrol is a vtl5c3/2. I pulled up the middle leg which is ground. No difference in volume

[chunkitup]

I checked the transistors and Q1,2,and 4 have the .6v drop but Q3 does not.


I replaced Q3 and still no change in volume. I am getting frustrated. I am ready to start smashing shit. Just venting. Its beautiful outside and I have to get this fixed.

Another difference from the scheme is the lead master is 25k and the rhythm pot is 44k.

[g1]

So you had mentioned earlier there was 26V coming out of the 560R7W resistor. But you don't have 26V at the EQ transistors. The schematic shows a pair of 1K2's paralleled in the supply, is there something like that? How about those 2 zeners at point H & I, are they ok?

[chunkitup]

I know I am trying to chase the path from the blue sec tap. The power resistor is for a different purpose. I have the path to the zeners but they are grounded in the middle and I get -15v from one zener to the eq section and the other zener gives me a +15v for another purpose.

Could there be a problem in the eq buss perhaps the J175(jfet)?

[Jazz P Bass]

With a signal into the FX return, does the headphone out work?
Those IC's use the -30 also.