5f4 tweed super build?

[MWJB]

If that resistor was 100K and the tube triode was drawing around 1.3mA (as it should) then .0013*100,000 = 130v drop from one end of that resistor to the other...and you don't have a 130v drop, you appear to have a volt or so.

The cathode resistor should be 1500 ohms, there aren't really any other resistors that you could confuse with a 1500 ohm, as there aren't any 15K or 150K resistors in the kit (or at least there shouldn't be). IF the cathode resistor really is 1.5K (you can check this with an ohmmeter, pull the tube & read from pin 3 to ground) then the tube is pulling 4.5mA...mutiply .0045 by 100 and you get 0.45volts. If that resistor was 1000ohms then you might see 4.5v drop from the top of the inverted V to pin 1...this is why I am thinking what I am thinking. If the 100K is right then the 1500ohm is wrong.

[chuckb]

I checked every 1.5k resistor on the board and they are all correct. When pulling the tube and checking the reading from p3 must the amp be on or off for this test?

Chuck.

[MWJB]

It's best to have the amp off for ohmage tests, but in the case of V3 pin 3 it shouldn't make any difference. What is the voltage at the junction of the inverted V made up of the 100K & 56K resistors feeding V3 pins 1 & 6?

[chuckb]

I checked p3 of v3 with the tube removed and got a reading of 0. This was taken inside the tube socket. I took a reading from p3 inside the amp on the tube socket and got no reading as well. the voltage reading I got at the junction of the 100k & 56k was 330v.

Chuck.

[Chuck H]

And he's tried a different tube in that socket. MWJB, good catch on the ay7 vs ax7 thing. I totally missed that.

Chuck and I have already been over the plate and cathode resistor issue. They've been checked and rechecked. At one point I almost wrote "just try replacing that resistor anyway". But That would have been insulting since this isn't Chuck's first build and I'm sure he knows how to read a meter. Now Chuck has gone ahead and replaced that resistor.

Both cathodes on V3 are high and so are both plates??? The relationship between pin 7 and pin 8 should be much closer.

What is the voltage on all pins of V3 with the tube pulled?

[chuckb]

Hey ChuckH, I took some voltages of v3 (PI) with the tube removed and here they are.

V3(PI) - p1=351.5v
P2= 0v
p3= 5v
p6=352.5v
p7=0v
p8=0v

Chuck.

[frus]

you probably have a miswire somewhere in that jumble of resistors and underside connections between the 16uF filter and 0.1uF cap. pin 3 should read zero with the tube pulled.

make sure that the underside wire between 100uF bias cap and junction of two 220k's is NOT connected to the junction of 1.5k and 56k (that goes to V3 pin 3 and presence pot), although in layout it looks like it almost should be. but that's just poorly drawn layout

[MWJB]

ChuckB wrote: "I checked p3 of v3 with the tube removed and got a reading of 0. This was taken inside the tube socket. I took a reading from p3 inside the amp on the tube socket and got no reading as well. the voltage reading I got at the junction of the 100k & 56k was 330v."

You want about 2v at V3 pin 3...did you get a reading of "0ohms" (dead short), or "no reading" (open circuit - poor ground connection?).

If the voltage at the junction of the 100K & 56K is 330v, how can you have 357v (more voltage) at the other end of these resistors? You need to measure all the dc voltages at all the pins of V3 at the same time for us to work out what is going on. It's easiest to take the voltage readings at the eyelets on the circuit board rather than stuffing probes in the socket pin holes.

Connect a jumper wire from ground to the end of the 1.5K at pin 3 V3, that is NOT connected directly to pin 3, what happens?

Also, do a continuity test (amp off) from V3 pin 3 to the junction of the 1.5K cathode resistor & the 56K NFB resistor (goes to speaker jack) and from V3 pin 3 to the RH tab of the Presence pot...both should read zero resistance/continuity. I'm wondering whether you have overlooked the connection between the presence pot RH tab AND the ungrounded side of the 1.5K to pin 3? If you just had pin 3 connected to the presence pot alone, reading from pin 3 to ground would show open circuit?

[chuckb]

Hey MWJB, I don't have that connection made from p3 of v3 to the neg side of the 1.5 resistor and from the 1.5 resistor to the presence pot. I have a direct connection from p3 to the RH lug of tthe prescence pot. I removed the wire from the pot and p3 and connected p1 to the neg side of the 1.5 then another wire from the 1.5 r to the RH lug of the prescence pot but the amp squeals like crazy when power is turned on.

Chuck.

[MWJB]

Do not connect pin 1 (plate, high voltage) to the 1.5K that should connect to V3 pin 3.

The wire from pin 3 V3 goes first to the hot (ungrounded) side of the 1.5K, junction with the 56K NFB resistor (connected to the speaker jack).=, then on to the RH lug of the presence pot.

If the amp squeals like this you need to reverse the blue & brown OT primary wires connected to 6L6 pin 3s.

[chuckb]

Hey MWJB, No I won't connect p1(TYPO), I did mean p3 of v3. I kinda figured the OT primary wires need to be reversed. I'll let you know what happens.

Chuck.

[chuckb]

Hey guys,
The amp seems to be working ok now. The lead from p3 of V3 wasn't connected @ the neg side of the 1.5k resistor. There is one small problem though with the Bass control pot. When the Bass is turned all the way off I have no volume, but when the Bass control is turned up I have all kinds of volume. Could it be that I have the lead going to the middle lug of the bass pot mixed up with the lead of the 1st lug of the treble pot?

Chuck.

[chuckb]

Hey guys, Well I did have sound on the bright channel but only for a brief time. I just turned on the amp again and both normal ch's are working but no bright ch's are. Also ,when the bass pot is turned down the vol is gone from the normal ch's as well. This also happened when the bright ch's were working as well. I guess I'll get this amp sorted out after awhile with your much appreciated help. Thanks again guys for all your patience and time.

Chuck.

[chuckb]

Hey MWJB, any suggestions?

[jmaf]

Double check your tone stack wiring, you may have something inverted. The bass control should not be able to ground all signal.