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Re: Military projector amp - speaker distorting/overworked

Posted: Wed 05/04/22 9:13 am
by Bieworm
Was planning to do that...

Ok, go to robrobinette.com tube bias calculator
Select tube type
Fill in plate to cathode voltage (=value when you subtract the cathode voltage from plate voltage)
Press calculate
Scroll down a little
Fill in number of tubes that share the cathode resistor
Fill in cathode voltage
Fill in cathode resistor value
Press enter
Look at the results

Re: Military projector amp - speaker distorting/overworked

Posted: Wed 05/04/22 10:05 am
by yello
JMPGuitars wrote: ↑
Wed 05/04/22 5:53 am
Tell him how you figured that out so he can do it. πŸ˜‰
Bieworm wrote: ↑
Wed 05/04/22 9:13 am
Was planning to do that...

Ok, go to robrobinette.com tube bias calculator
Select tube type
Fill in plate to cathode voltage (=value when you subtract the cathode voltage from plate voltage)
Press calculate
Scroll down a little
Fill in number of tubes that share the cathode resistor
Fill in cathode voltage
Fill in cathode resistor value
Press enter
Look at the results
Perfect, thank you. That is the calculator I had tried, but hadn't put the numbers in right. I now get the same 90% result.

Getting close, just need to work on the input jack area.

Re: Military projector amp - speaker distorting/overworked

Posted: Wed 06/01/22 1:56 pm
by yello
Now that my 18w build is done, I went back to finishing up the last 1% of the military amp.

I added the 10k resistor from input to v1, and also ended up doing separate 1k 5w screen resistors. And added a v2 bypass cap as I didn't have the part on hand when I did the others. Will test with these new components in, then am going to test a PPIMV too, then that should do it for this one.

Re: Military projector amp - speaker distorting/overworked

Posted: Wed 06/01/22 2:25 pm
by Bieworm
yello wrote: ↑
Wed 06/01/22 1:56 pm
Now that my 18w build is done, I went back to finishing up the last 1% of the military amp.

I added the 10k resistor from input to v1, and also ended up doing separate 1k 5w screen resistors. And added a v2 bypass cap as I didn't have the part on hand when I did the others. Will test with these new components in, then am going to test a PPIMV too, then that should do it for this one.
So... what's next?πŸ˜‰

Re: Military projector amp - speaker distorting/overworked

Posted: Wed 06/01/22 3:09 pm
by yello
Bieworm wrote: ↑
Wed 06/01/22 2:25 pm
yello wrote: ↑
Wed 06/01/22 1:56 pm
Now that my 18w build is done, I went back to finishing up the last 1% of the military amp.

I added the 10k resistor from input to v1, and also ended up doing separate 1k 5w screen resistors. And added a v2 bypass cap as I didn't have the part on hand when I did the others. Will test with these new components in, then am going to test a PPIMV too, then that should do it for this one.
So... what's next?πŸ˜‰
Well, good question. I have a nice pile of potential amp projects on hand, here are a couple:

1) Mojotone 5f2a tweed Princeton kit
2) Transformers for Fender Deluxe Reverb
3) Hammond AO-35 and AO-48 chassis and tubes which could be 18w fodder
4) Filmosound 385 that is half-modded

I'm leaning towards doing the Princeton first as I have 100% of the parts on hand and it should be fairly simple. Or I might finish up the 385 first, then do the Princeton.

For my next 18w type build, those hammond chassis will be fun to do up, just need to select an ideal circuit for each. AO-35 is dual 12ax7, dual el84 and 5y3. AO-48 is 12dw7, dual 12ax7, ef86, dual el84, ez81. Would be fun to do up the AO-48 with Reverb, whatever the circuit is.

Re: Military projector amp - speaker distorting/overworked

Posted: Fri 06/03/22 1:34 pm
by yello
Bieworm wrote: ↑
Wed 06/01/22 2:25 pm

So... what's next?πŸ˜‰
Actually, what I would love to do next is to make a layout diagram of the military amp. One that reflects all of my mods and changes and is laid out for a traditional turret board build in a typical chassis. Not sure where to start as turning a schematic into a layout is currently over my head!

Re: Military projector amp - speaker distorting/overworked

Posted: Sat 06/04/22 3:00 pm
by yello
Finally got a chance to plug in and play at full volume. The latest mods changed it quite a bit. It is way louder, lots more gain, and quite bright.

I assume volume and gain are from the cathode bypass cap on v2, and brightness from the 10k between input and v1? Or those things in relation to everything else.

I need to try some different tubes to find a good one that’s not microphonic in v1. Then I will try the PPIMV mod.

Re: Military projector amp - speaker distorting/overworked

Posted: Sun 06/12/22 2:44 pm
by zaphod_phil
yello wrote: ↑
Sat 06/04/22 3:00 pm
Finally got a chance to plug in and play at full volume. The latest mods changed it quite a bit. It is way louder, lots more gain, and quite bright.

I assume volume and gain are from the cathode bypass cap on v2, and brightness from the 10k between input and v1?
I think your assumptions are about right. However, I doubt that reducing the input grid stopper to 10k would have made for a large increase in brightness.Maybe that's the combined effect of all your changes.

Keep on rockin!

Re: Military projector amp - speaker distorting/overworked

Posted: Wed 06/15/22 3:51 pm
by zaphod_phil
How about shooting a quick video on your phone and posting it on You Tube :)

Re: Military projector amp - speaker distorting/overworked

Posted: Mon 09/12/22 3:44 pm
by yello
I'm circling back on this amp, to capture all the work that went into, and the huge amount of generous advice I got from 18w members, by making a visual layout. I'm starting with the stock amp (minus the unused projector oscillator bits). From there I will do a second layout that captures all of the mods that we did to it.

I have left off the obvious bits like heater wiring, power switch/IEC/fuse, speaker wiring, etc. just trying to get the circuit part captured. I'm not done yet, hopefully what I have so far is correct (I mostly understand schematics at this point) - though I'll admit to being lost on the tone circuit. It is a 5 position rotary switch and I just can't make sense of it yet. Ultimately I will want to simplify the tone circuit, either to just the middle ("normal") position of that 5 way switch hard-wired, or maybe a 3-position tone switch that picks positions 1, 3, and 5.

I'd love help some to get the stock tone control layout right.

And this is the original schematic:

Image

And the original schematic, trimmed to remove the unused bits:

Image

Re: Military projector amp - edited 9/13/22 layout help needed

Posted: Wed 09/14/22 4:44 pm
by yello
This is a closer photo of the 5-position tone control rotary switch that I can't figure out how to draw in layout format:

Image

Re: Military projector amp - edited 9/13/22 layout help needed

Posted: Thu 09/15/22 7:59 pm
by JMPGuitars
I draw components for layouts by looking at the actual component in the amp. Take good photos of it if it's hard to see.

Re: Military projector amp - edited 9/13/22 layout help needed

Posted: Fri 09/16/22 9:25 am
by yello
JMPGuitars wrote: ↑
Thu 09/15/22 7:59 pm
I draw components for layouts by looking at the actual component in the amp. Take good photos of it if it's hard to see.
It's definitely hard to see, given the way every wire for the components comes out from behind the turret board!

Re: Military projector amp - edited 9/13/22 layout help needed

Posted: Fri 09/16/22 2:31 pm
by JMPGuitars
yello wrote: ↑
Fri 09/16/22 9:25 am
JMPGuitars wrote: ↑
Thu 09/15/22 7:59 pm
I draw components for layouts by looking at the actual component in the amp. Take good photos of it if it's hard to see.
It's definitely hard to see, given the way every wire for the components comes out from behind the turret board!
There are quite a few rotary switch types. As long as you can find the type of switch, the rest is a matter of confirming with the schematic what connects where. And for the layout, you make that clearer than reality.

Re: Military projector amp - edited 9/13/22 layout help needed

Posted: Sat 09/17/22 4:16 am
by Bieworm
You first have to figure out the way the connections work on the switch. There should be 2 common terminals which connect to one other with every switch.

Draw this out... and then figure out which components should interconnect