Todd

I found the problem with the voltage. I was the jumper wire from the filter cap to the 220K resistor.  It was either soldered badly(likely) or the wire was not up to the job current wise.  ANyway I now have 149V at this point!

I still have an issue with getting any decent volume out of the amp.  I think this is again to do with bad wiring round the input jack area, because if I wiggle the guitar jack in the socket I briefly get some good volume.

I am going to re-do my wiring in this are and replace all the tone and volume pot wiring with upgraded wire.

I will post a gut shot, but I'm nervous about it as my wiring is very poor, I will take some pics at the weekend.

Appreciate your advice so far Todd, its been a big help.

 

replaced the capacitor and 221K resistor (the original spec was for 220k) with a 220 K resistor... still only getting 74V after the resistor instead of 149  but the voltage I'm getting before the resistor is 274v maybe the jumper wire from the filter capacitor is the issue? ... the hunt continues..

Todd

Already started on re-doing the wiring.  Should complete that today.  This is my first real amp build. I'm using this a prototype to work out best location of valves , components etc. So I see this as all part of my learning.

The frustrating part is getting mu soldering skills to a high enough standard that I am happy with it.

Todd

I found one fault on the input jacks that is causing the guitar signal to go to ground! Poor soldering.  I have ordered the correct Capacitors.  They should arrive tomorrow. I'll re-solder the input jacks.  I am now getting some guitar ... but at low volume. At least this is a step forward !

Doesnt explain my issue with the low voltage though as there seems to be plenty voltage before the 200K resistor immediately before pin1 on Tube 1. and the resistor seems to be OK.  it is only .5W maybe a need a 1W resistor there?

Cheers

Stuart

Readings from my amp (in brackets)

Tube   Type   Pin1   Pin2   Pin3   Pin4   Pin5   Pin6   Pin7   Pin8   Pin9
                              
V1   12AX7   149 (73)      1.4 (1.56)         149 (73)      1.4 (1.56)   
                              
V2   12AX7   191 (148)      1.5         317 (298)   191 (149)   192 (152)   
                              
V3   12AX7   237 (172)      65 (62)         242 (172)      65 (62)   
                              
V4   EL84         12 (11)            335 (325)      340 (326)
                              
V5   EL84         12 (11)            335 (326)      340 (320)
                              
V6   GZ34            281 (237)      281 (238)         
                              
OT CT   340   

I looked at the V1 pins 1 and 6 as this obviously well out and I noticed I have an incorrect capacitor that feeds pin 1 it should be a .0015uF and I have a 0.000015 would that make that voltage difference? I ordered the wrong caps... so have put in an order for the correct ones.

I guess this might have a knock on effect on the rest of the pre-amp circuit?

Does it explain why I get no guitar sound at all from my amp?  all I get is a hum... which increases in volume as I increase volume and master pots?  I suspecta grounding issue or perhaps output transformer not wired correctly?

Any help would be very welcome!

Thanks

Stuart....

                        

Todd

I'll post my readings tonight...

It looks like I have an issue with my driver/phase invertor tube (tube 3)  ...  one of  the two 100K resistors that feed onto pins 1 and 6 are failing.  I replaced them by 1W resistors as I was worried half watts would not be good enough, but still pin 6 resistor reads very low/fails. My valve amp guru is in hospital so I dont really have anyone to turn to!  So hope you guys can help me

Cheers

Stuart

Stuart

Well I certainly have some differences in my voltages at these test points. I'm using 240V obviously which is what the spreadsheet has as input voltage.

I'm using the ceriatone schematic and getting the components etc myself.

Looks like I have some debugging/fault finding to do.

Stuart

Thank you so much ... this is a big help

If anyone has these ...then I'd love that info myself as I'm nearly completion of my lightning build... getting ready to power it on tonight.!

Cheers from Scotland!

Stuart