liverpool done but need some help

[pinkmarkos]

hey guys- i just finished a brand new liverpool today. it fired up wonderfully following the express build guide with bulb limiter and everything except for letting a little smoke out the first power up. My heater wires had shorted to each other, but I couldn't see it. Needless to say, smoke in about 2 seconds. After fixing that however, there is another problem- i am not getting any bias voltage on both sides of V1, or the power tubes. i can't figure out why this would be. The amp itself is not nearly as loud as it should be, it's very quiet and clean until about 10 o'clock then breaks up very gradually until dimed. I swapped out two sets of pre-amp tubes, and my power tubes are known good ones. I am using a 33k grid stopper on V1(worked great on the express). if anyone could help, i would really appreciate it. here are the voltages i am getting-
V1 Plate- 183, cathode- 0, plate 1b- 182, cathode 1a- 0
V2 Plate- 254, cathode- 45
V3 Plate- 208, grid- 45, cathode- 61 Plate 1b- 205, grid 1b-40, cathode 1b- 61

V4-V7 Plate 341, screen 320, Grid bias- 0
all heaters 6.4 vac
B+1- 344, B+2- 325, B+3- 273, B+4- 259, B+5- 246

I checked all the connections including runners under the board, i double-checked that all the pots are the correct values, i think i checked all resistor and cap values for correctness. the amp itself is very quiet in terms of hum and buzz, way quieter than my express. BTW- thank you to allyn for the chassis, RJ for the boards, and toneslut for the trannies. great products and great service!! here are some pics:

[M Fowler]

Reflow the solder on VR1 where C7/R5 ground, the other end of this cap/resistor go to pin 3 cathode on V1. Also check that ground buss.

Mark

[pinkmarkos]

mark- I looked at/reflowed the solder joint at the ground of C7/R5- didn't help. The ground buss appears to be good- I even sandpapered the buss and the back of the pots when I put it together to create better contact. I checked the cathodes of V1 and i got 1 volt and 1.5 volts respectively, so they are getting some voltage. also, on the power tubes, pin3 (cathode) is getting 10 volts, but still getting nothing on the control grid. I will replace the couple of wires that are operating above their voltages that supply the power tubes, and check around for other errors. In general- this amp should be on par with the express as far as volume and gain right? as it is now, it just seems too quiet. any other suggestions would be most welcome. thanks- Mark

[fishy]

e power tubes, pin3 (cathode) is getting 10 volts, but still getting nothing on the control grid.

Are you looking for a DC level on the control grids?
Isn't this cathode biased?

[M Fowler]

I got to thinking about your amp and you should only have around 1.7 on pin 3 V1; 182 on pin 3 V2, and 57 on pin 3 V3.

Control grid pin 2 and 7 V3 should be around 55.

EL84 pin 3 should be 10.

Yes this amp gets plenty loud at 30 tube watts so there is a problem.

Mark

[M Fowler]

Check your screen voltages V4-V7 pin 9

Mark Abbott gave his Liverpool voltage chart as,

B+1=335vdc
2=312.5vdc
3=260.1vdc
4=244.5vdc
5=231.1vdc

Plate voltage=325
screen voltage=307
bias voltage=-9.42 vdc

I don't have mine not sure what I did with them. Hope this helps.

Mark

[pinkmarkos]

Mark- I had actually found that particular voltage list via the search function, so i knew i was in the ballpark- about 10-15 volt above those readings. from your calculations, the only one off now is V2 pin 3- i am significantly low at 45VDC. i can't picture how this would affect the signal amplification, but maybe the missing volume is originating from this area.
also- why would you not find any DC voltage on the power tube control grids in a cathode biased amp? is it analagous to V1 where you only have a grid voltage when signal is coming from the guitar?
i A/B'd this amp with my express and it is definitely quieter. the express shakes the walls at 12 o'clock, but the liverpool, although it actually sounds really great, is much quieter. i had improvement in volume by switching around the pre's, but not much.
BTW- i am getting 320VDC on the screens, and 341 VDC on the plates. thanks again for helping! MP

[dartanion]

Not that this is the issue at hand, but your bright switch wiring looks a bit suspect. I looks as if you are shorting out signal to ground as one of the cap leads appears to bridge between the wiper and ground leg of the volume pot.

I'll look more closely at your photos and see if I can find anything else that looks suspicious.

[pinkmarkos]

dartanion- thanks for any input, really! i was wondering about this wiring configuration myself because the express bright switch is wired differently. you can't see it from the angle of the picture, but there is clearance between the cap leads and the ground lug of the volume pot. i was thinking i might go back and rewire express style though with the shrink tubing, just to be sure. BTW- i am using 110 pf and 330 pf values and they sound great.
i was also thinking the lower volume might be my impedance switch. i used a different kind this time because i had problems wiring the BOM switch correctly, so maybe i will try direct wiring to the jacks.

[M Fowler]

I used the 330pf also for more bass response.

There should be 180v on pin 3 V2

Mark

[M Fowler]

Carefully check the circuit for pin 1, 2, and 3 on V2 as your B+4 is at 259v so that is good but your cathode on V2 should be around 180v not 45.

Mark

[fishy]

180v on a cathode of a 12Ax7 without elevated heaters would probably kill the tube.
The cathode resistor is also only a 10k. I think 45v looks high already.
I believe Ron put example voltages in the Express voltage chart and for this area of the amp, you should be able to go by that value for a good ballpark figure.
2 - 3v would seem more realistic to me but I'm pulling that from thin air.

Does the 10k cathode resistor actually measure 10k?
Is the ground good on thats stage of the amp?

[pinkmarkos]

fishy- i think you may be on to something with that 10k cathode resistor to V2. i am at work now so i can't check anything until the morning. i wasn't aware that the express voltages would apply to the liverpool's preamp section, so i will use those as a guide. thanks again for everyone's input MP

[M Fowler]

Well I didn't find any Liverpool charts but here is the Rocket chart.

I was going by both the TW and AC 30 which explains why I had V2 at 182 instead of V1.

[ontariomaximus]

My guess is your cathode resistor on the 3rd stage is not 10k but 100k