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Messages - g1

#766
  The point marked +9 goes to ground.  The points marked with ground symbol go to your negative supply voltage.  The TL071 should be able to handle up to 36V difference between pins 4 and 7 so you should be fine.
As you see, pin7 will still end up being "positive" in relation to pin 4.
Pin3 still ends up being at half the supply voltage (due to R1/R2 voltage divider).
#767
Quote from: galaxiex on July 29, 2014, 02:29:17 PM
3 wire cord is in the plans but I was unsure how that works with the Pos voltage on the chassis????
There is no voltage on the chassis.  It is positive ground.  The supply is negative instead of positive.  Many old cars used to be positive ground.
  Voltage and ground can be tough to wrap your head around, all voltage is relative to something, we usually use ground as that reference, but it is not necessarily so.
  In this case, everything is in reference to the positive, so we call that ground, and you will be connecting that point to the chassis.
#768
Tubes and Hybrids / Re: ampeg vt-22 PI
July 15, 2014, 12:26:39 PM
Ok. the 12DW explains the PI imbalance, as you proved by trying the 12AX and finding it was balanced. 
Yes, you can plug 6L6's right in with this circuit.  Just have to be good enough to handle the high plate voltage.
Of the old tubes, not likely they are all bad, try them one at a time, probably the one or two that redplate are pulling down the bias for the others.
#769
Tubes and Hybrids / Re: ampeg vt-22 PI
July 14, 2014, 08:58:01 PM
Triple check that both side heaters are lit.
Remove PI tube, power off.  Measure resistance from pin 8 (at the socket not at the board) to ground.
Now measure resistance from socket pin 6 to point D of power supply resistors.
#770
  Sorry to nitpick, but standard "safe" wiring of fuseholder is for incoming power to go to back end of fuseholder first, then out the side.  This is so as soon as the fusecap is disconnected the hot can no longer touch anything.  With the hot on the side terminal like you have it, as the fuse is being pulled out it can contact the "hot" side terminal.
Of course we assume the unit will be unplugged before the fuse is removed, but mistakes happen.
#771
Tubes and Hybrids / Re: sound city clean-up
July 04, 2014, 12:27:22 PM
Quote from: ilyaa on July 03, 2014, 04:49:28 PM
if i just pull v4 out and play without a tube in that socket, will the amp be mad?
Should be fine, preamp supply voltage will probably come up a little.
#772
Quote from: ilyaa on July 03, 2014, 03:19:45 PM
QuoteWhere are you getting those "should be" voltages from?  Are you using a different schematic than the one from your first post?

its a classic A, not a classic B, i discovered

the new schematic is attached above (in my post that starts with NOTE:)
Ok, got the correct drawing now, sorry about that!
One thing very critical for power is screen supply.  Have you checked the voltages at pin 4 of both power tubes?
#773
Quote from: ilyaa on July 02, 2014, 11:33:38 AM
on the power supply end of the 82K 1W resistor, the voltage looks high (should be 460 and its at about 490), but on the PI end, its low (should be 300 and its only 260). the collectors of the PI transistors are a bit low at 130-140V, instead of 150.
Where are you getting those "should be" voltages from?  Are you using a different schematic than the one from your first post?
#774
Quote from: BrianS on June 29, 2014, 01:08:42 PM
I got to thinking a little bit and decided to disconnect the primary wires of the PT from the amp and measure that way.  Doing this, I get 29vac. 
I think you mean the PT secondary?  So when it's connected to the board it reads 3.4VAC, but when disconnected it reads 29VAC?
Is the fuse blowing?
#775
  There are no parts missing.  The points you are looking at are where the reverb cable would go if it were mounted from the component side.
I have circled on your picture where the 2 cables would  connect, the pair on the left goes to tank input, on the right to tank output.
  It looks like you have them connected to the same points (but double check), just mounted from the solder side rather than component side. 
#776
  I have had new caps like that with some kind of white powder on them, it's not leakage.  Generally you only see issues like that with electrolytics.
#777
  I think where you said preamp in jack, you meant power amp in?
You may still have an issue with the power amp in jack, give it another shot of cleaner and work a cord in and out of the jack several times.
See if it makes a difference.  If not, try connecting preamp out jack to power amp in jack with a patch cord.  Then try playing through the regular input again.
#778
  Stick with 1458's and see if it improves reliability.
Normally 4558 is ok to sub for 1458.  However, there are odd cases where they don't work well, and if I'm remembering correctly, the only place they seem to have issues is in some Marshall amps.  I can't remember which models or why it is a problem.  I think I have seen Enzo mention the same issue and he may remember more details.
#779
  If the ripple is so low that a good meter will not accurately measure it, then it is not a concern. 
Yes, it is nice to be able to see it on a scope, but if there really is a problem, it should show up on the meter as AC volts.
#780
The Newcomer's Forum / Re: 2A473j value
May 24, 2014, 03:11:04 PM
  Yes, 100nF and 47nF.  They should also have a voltage marked on them.  Do not use them in a circuit that will exceed the voltage rating.