V2 - pin 7 question

[catoclepa]

Ciao a tutti......hallo to everyone from Italy.This is my first post on this comunity i follow with great interst for year. I built some marshall amp on the past and now i just finished my first tweed deluxe.
I'm testing some configuration with sovtek 5y3 gt and GE 5y3 gt Nos
and 12ax7 or 12a7t on V1: tension value generally get close enough the norm. The amp saund great to about half volume .A louder the sound gets a strange distortion noise like metal ZZZZZ .
There are two things that are not regular: the first! voltage in pin 7 - V2 is only 2.9 v ( tray to resolder wire, change v2 , change the 1 mhom resistor, change the 0.022 capacitor......nothing!!!! remain 2,9 volt)
the second: i have only 5.1 volt on filament.I think the cause is the trasformer that input should be 240 volts, but in Italy we have 220/230 volts.So the trasformer provide 5.8 volt without valves connected .
I checked each wire and all solder and seem ok.
these voltage values measured with Sovtek 5y3Gt 2x 12axt 2 x 6v6Gt tung Sol

V1
pin1 155 v
pin3 1.2 v
pin6 156 v
pin8 1.2 v

V2
pin1 154 v
pin3 1.1 v
pin6 182 v
pin7 2.9 v
pin8 42 v

V3/v4
pin3 341 v
pin4 304 v
pin8 21 v

V5
pin8 352 v ( 292 on STB)



thank in advance anyone who will give me directions to solve the problem

Sergio

B+A 347 v B+ B304 v B+C 235v

[loudthud]

The voltage on pin 7 of V2 will not measure correctly because the meter will load down the voltage thus changing the bias on the tube. When you connect your meter's probe to the circuit, the tube operates differently than it does when the probe is not connected.

Since you measure 42V on pin 8, I think your amp is working correctly.

If you had 2 meters and connected 1 to pin 8 you would see that when you connected the other to pin 7 that the voltage on pin 8 would fall from 42V to about 4V. This is normal.

[catoclepa]

thanks for your very comprehensive reply: I'm worried for nothing!
What do you think about the partridge sound that is putting out the volume from 7 onwards?

[loudthud]

I do not understand what you mean by "partridge sound". Do you mean too much bass? This is a problem many people have with the 5E3. Try replacing the 0.1uF capacitors with 0.022uF.

[catoclepa]

the amp sounds very good to about half volume(volume knob value 7/8).
increasing the volume the sound takes a strange distortion, but not the classic crunch! A kind of metallic sound very similar a big buzzzzzzz.this strange sound remains the same even when, or tried to replace my Sovtek 5Y3 with a GE nos and changing my v1 tungsol 12AX7 with a 12AT7 nos.
I checked with the meter value of each resistance and as soon as I get the capacitors mallory try substitutes existing Orange Drop. I disconnected every wire and connected everything again , re-check every solder....but the strange suon/distortion remain the same.I have exhausted the resources and do not know what else to try to do!only remains to try to change 6v6gt
thank you for support!

[tubeswell]

If the buzzing is associated with volume change, then its probably some oscillation, and possibly from lead dress or grid current somewhere (or both). Try 10k-100k grid stopper(s) at pins 2 and 7 of V2. Also try moving the (signal) wires to the grids around a bit, or try shielding them

[catoclepa]

Same problem remain

I found this two article on the net :
Grid Resistors
and
The Valve Wizard.

I understand that to speak of to put grid stopper value 470 k on v1 preamp.
I followed your advice and I replaced the wires to pins 2 and 7 with shielded cable both V1 and V2. the strange sound is slightly decreased but not disappeared completely. now appears with the volume at 8.
I also tried to replace all the orange drop capacitors with Mallory and I also tried a 12ay7 EH in V1.I also replaced the pots CTS with pots ALPHA(just to leave no stone unturned).I will only have to try to put grid stopper on V2 pin 2 and 7 but I'm not sure of the value and if it is the right thing to do!