Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hesamadman on June 05, 2015, 09:51:07 am
-
I have not done this before but in my next build I want to try some gain stages in parallel. It seems pretty straight forward but figured I would ask. Is this correct?
Was wondering if I needed another CC between 6 and 1, in which case maybe use 2 .044?
-
If I'm understanding right, you actually just connect plates, grids, and cathodes. You only need 1 cathode resistor and 1 plate load resistor. Signal goes into the shared grids, comes out of the shared plates. You don't want 2 plate load resistors as you have them drawn, because they'd be in parallel.
When I have the room for the extra tube/gain stage, I really like the paralleled input stage (and why is paralleled so hard to spell??) It "seems to" make a fatter sound imo.
-
(and why is paralleled so hard to spell??)
HA HA i am with you 100%
It "seems to" make a fatter sound imo.
This is what I am going for. Absolutely
You don't want 2 plate load resistors as you have them drawn, because they'd be in parallel.
This makes perfect sense.
You only need 1 cathode resistor
I would like to toy around with different values of these so I wasn't planning on sharing. I know my schematic shows the same values for both, but the design I have drawn up is dependent on different values for each triode. Hoping to yield positive results. :icon_biggrin:
-
Are you thinking to put a switch as to parallel tubes ?
if so, it will be better don't use it if the amp is on or you hear a loud pop
---
Vox in the AC30CC2 simply connect together the input grids of the two triodes
each triode has a dedicated plate resistor (R6 and R7) and cathodes share a single resistor (R4)
http://el34world.com/charts/Schematics/files/Vox/Vox_AC30CC_Service_Manual.pdf (http://el34world.com/charts/Schematics/files/Vox/Vox_AC30CC_Service_Manual.pdf)
I think you cal leave the 2 plate resistor and use two separated cathode resistors and bypass cap as to have each triode voiced differently
then you can join the two input as to have a mix of tone and a boost in gain
K
-
I would like to toy around with different values of these so I wasn't planning on sharing. I know my schematic shows the same values for both, but the design I have drawn up is dependent on different values for each triode. Hoping to yield positive results
In Merlin's book he has a chapter dealing with the paralleled tubes and the "mixing resistor" on the cathodes. I *think* he has a circuit using a pot to shift back n forth, or something like that. Definitely worth playing with, I'd think.
-
I would like to toy around with different values of these so I wasn't planning on sharing. I know my schematic shows the same values for both, but the design I have drawn up is dependent on different values for each triode. Hoping to yield positive results. :icon_biggrin:
Then you're going for a pseudo Plexi input that's had the input jack's coupled together? The benefit is having control over both stages via a vol control for each to be able to mix them together at will. If not your design will be much more limited not wringing out all the benefit of doing this. That is, if this is your main goal/idea? If you just parallel the tube sharing the resistors and remember to halve the values you would normally use for a single triode to yield the same load line.
-
I know that you need to halve the value of a shared cathode resistor to achieve the same bias point.
You can have separate plate resistors provided that each anode has its own coupling cap going toward the next stage. Just tie the coupling caps together. (Did this) You also can have separate cathode resistor/bypass cap networks for the two triodes.
Do you have to also halve the value of the plate resistor of it is shared by the two triodes? IOW 50K instead of "standard" 100K.
I think it would be interesting to have one typical triode with 100K plate resistor and 1.5K cathode resistor coupled with a second triode with 220K plate and 2.2k (or 2.7K). Perhaps a relatively small bypass cap on the "standard" triode and a larger bypass cap on the other. An on-on-on switch could bypass a large resistor under the cathode network for one, the other, or neither triode.
Cheers,
Chip
P.S. I couldn't find Merlin's discussion of parallel preamp stages online and don't have access to my copy of his preamp book.