norburybrook wrote: ↑Sun Feb 16, 2020 7:43 pm
Oh Shit....here we go ..do I have to build another amp soon?
well done fellas
M
NO!
thanks for that tony...I'm updating my studio at the moment and that's taking all my time and money!!!!
I think as someone pointed out earlier this need moving to a new thread topic and hopefully a sticky in the files section when the schematic and layout have been done.
Why do you have 2 40K resistors in series coming off the main filters feeding the PI you only need the one
BTW. Can you somehow highlight the parts in question on your schematic so both seeing the same thing
I think the 470K bleeders look fine
T
Last edited by talbany on Mon Feb 17, 2020 11:38 am, edited 1 time in total.
" The psychics on my bench is the same as Dumble'"
talbany wrote: ↑Mon Feb 17, 2020 11:31 am
Why do you have 2 40K resistors in series coming off the main filters feeding the PI you only need the one
T
Tony, there are 2 on the parts list. I have this as one of my listed questions. Where should the second 40K go? Maybe the dropping resistor for the PI Driver?
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talbany wrote: ↑Mon Feb 17, 2020 11:31 am
Why do you have 2 40K resistors in series coming off the main filters feeding the PI you only need the one
T
Tony, there are 2 on the parts list. I have this as one of my listed questions. Where should the second 40K go? Maybe the dropping resistor for the PI Driver?
Not sure yet? omit the 1 for now and highlight the parts in question on your schematic your talking about so we are both looking at the same part and I'll cross it with what I have
BTW..I think the 470K bleeders look fine
T
" The psychics on my bench is the same as Dumble'"
Tony, there are 2 on the parts list. I have this as one of my listed questions. Where should the second 40K go? Maybe the dropping resistor for the PI Driver?
The description in the parts list "Shunt resistor preamp power supply" implies that one of the 40Ks would be connected to ground, forming a voltage divider.
Maybe like this...
40K.png
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Last edited by sluckey on Mon Feb 17, 2020 11:58 am, edited 1 time in total.
There you go. I added a note in green. Just to recap Questions pending:
1) bias network on the PI, are my 2x10K, 2x30k correct? Where should the 47K go?
2) where should the extra 1M go on the tremolo
3) on the pentode is the .1uF going to cathode or ground on the original
4) on the supply there are 6x470k, so the 2x47uF (350V) are indeed stacked. Does my current schematic look good? Any ideas on the 2x 40K (5W) and how to go about the PI driver (which doesn’t have a dropping resistor listed and also is missing a cap supply)
5) the lnfb on the reverb, is the 10k inside or outside? I’ve seen amps taking both approaches
6) The reverb entrance, Bill's schematic has it as per my green line, I used the standard approachm which for me makes more sense. Which is correct?
7) I think the 220K on the reverb return is as per AB763 (mixing resistor), and not after the decoupling as per Bill's schematic.
EDIT: updated schematic further down the thread
Last edited by Bombacaototal on Mon Feb 17, 2020 12:50 pm, edited 1 time in total.
Tony, there are 2 on the parts list. I have this as one of my listed questions. Where should the second 40K go? Maybe the dropping resistor for the PI Driver?
The description in the parts list "Shunt resistor preamp power supply" implies that one of the 40Ks would be connected to ground, forming a voltage divider.
He calls all dropping resistors on the parts list as shunt, so I dont think this is an indication of a votlage divider.
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Last edited by Bombacaototal on Mon Feb 17, 2020 12:05 pm, edited 1 time in total.
Tony, there are 2 on the parts list. I have this as one of my listed questions. Where should the second 40K go? Maybe the dropping resistor for the PI Driver?
The description in the parts list "Shunt resistor preamp power supply" implies that one of the 40Ks would be connected to ground, forming a voltage divider.
Yeah I saw that but I don't think so?
That would drop too much Voltage there. Dumble usually has an 820K Shunt resistor (voltage divider) there to set the RC time constant. On his ODS's
Thanks for the revised sch.
" The psychics on my bench is the same as Dumble'"
He calls all dropping resistros on the parts list as shunt, so I dont think this is an indication of a votlage divider.
I do. The preamp B+ string is being fed by 700V. The 40K/40K divider would cut that in half. 350V would be much more reasonable to feed the little tubes.
40K.png
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Tony, there are 2 on the parts list. I have this as one of my listed questions. Where should the second 40K go? Maybe the dropping resistor for the PI Driver?
The description in the parts list "Shunt resistor preamp power supply" implies that one of the 40Ks would be connected to ground, forming a voltage divider.
He calls all dropping resistors on the parts list as shunt, so I dont think this is an indication of a votlage divider.
Thanks I got that but I what about the others (.1 and 220k etc)
" The psychics on my bench is the same as Dumble'"
sluckey wrote: ↑Mon Feb 17, 2020 11:48 am
The description in the parts list "Shunt resistor preamp power supply" implies that one of the 40Ks would be connected to ground, forming a voltage divider.
He calls all dropping resistors on the parts list as shunt, so I dont think this is an indication of a votlage divider.
Thanks I got that but I what about the others (.1 and 220k etc)
On the Pentode tube he calls .1uF as Dry Amp Screen Bypass Capacitor. On the reverb there are 4x 220K called "Reverb Send Amp Feedback Serial Resistor", "Reverb Return Amp input terminating resistor", "Reverb return amp cathode resistor" and "Reverb Return Amp output serial resistor" (which is the one on my question - which I assume is like Fender and not like Bill).
Is that what you were asking?
Last edited by Bombacaototal on Mon Feb 17, 2020 12:23 pm, edited 3 times in total.
He calls all dropping resistors on the parts list as shunt, so I dont think this is an indication of a votlage divider.
Thanks I got that but I what about the others (.1 and 220k etc)
On the Pentode tube he calls .1uF as Dry Amp Screen Bypass Capacitor. The 220K which are grids he calls Feedback Serial Resistors. Is that what you were asking?
Yes are they on the schematic already or did you completely omit them and are just not sure where they go I don't have the parts list with me?
Tony
" The psychics on my bench is the same as Dumble'"
Everything is on the schematic already or has a note about it in green, except for the PI Driver supply given it doesnt have a cap or dropping resistor listed on the parts list.
The missing 1M on the tremolo is not listed (maybe I should add a note in green). He calls it "Tremolo Oscillator operation control resistor".
Other than that the entire parts lists is listed on my schematic and you do not need to go through it again.
Note that there are some mistakes on the parts list, for example the PI plates are listed as 120R instead of 120K, the presence pot is listed as 500R instead of 5K, there is a cathode resistor on the reverb return is listed as 220K instead of 2.2K, etc. I have added the "corrected" logical values to my schematic
