Military projector amp - speaker distorting/overworked

Forum to discuss amp circuits besides the 18 Watters and their ilk.

Moderators: JMPGuitars, CurtissRobin, colossal, zaphod_phil, Daviedawg, Graydon

Post Reply
User avatar
Bieworm
Verbose Wizard of Oz
Verbose Wizard of Oz
Posts: 1749
Joined: Mon 02/10/20 8:24 am
Location: Belgium

Re: Military projector amp - speaker distorting/overworked

Post 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
2 x
"THIS should be played at high volume..preferably in a residential area"

User avatar
yello
Occasional poster
Occasional poster
Posts: 143
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Military projector amp - speaker distorting/overworked

Post by yello »

JMPGuitars wrote:
Wed 05/04/22 5:53 am
Tell him how you figured that out so he can do it. 😉
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.
2 x

User avatar
yello
Occasional poster
Occasional poster
Posts: 143
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Military projector amp - speaker distorting/overworked

Post 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.
1 x

User avatar
Bieworm
Verbose Wizard of Oz
Verbose Wizard of Oz
Posts: 1749
Joined: Mon 02/10/20 8:24 am
Location: Belgium

Re: Military projector amp - speaker distorting/overworked

Post 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?😉
0 x
"THIS should be played at high volume..preferably in a residential area"

User avatar
yello
Occasional poster
Occasional poster
Posts: 143
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Military projector amp - speaker distorting/overworked

Post 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?😉
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.
1 x

User avatar
yello
Occasional poster
Occasional poster
Posts: 143
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Military projector amp - speaker distorting/overworked

Post by yello »

Bieworm wrote:
Wed 06/01/22 2:25 pm

So... what's next?😉
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!
1 x

User avatar
yello
Occasional poster
Occasional poster
Posts: 143
Joined: Thu 09/03/09 2:00 am
Location: Unknown

Re: Military projector amp - speaker distorting/overworked

Post 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.
1 x

User avatar
zaphod_phil
Builder, Admin
Builder, Admin
Posts: 15200
Joined: Wed 03/19/03 2:00 am
Location: YYZ

Re: Military projector amp - speaker distorting/overworked

Post 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!
1 x
Nature abhors a clean tube amp

User avatar
zaphod_phil
Builder, Admin
Builder, Admin
Posts: 15200
Joined: Wed 03/19/03 2:00 am
Location: YYZ

Re: Military projector amp - speaker distorting/overworked

Post by zaphod_phil »

How about shooting a quick video on your phone and posting it on You Tube :)
1 x
Nature abhors a clean tube amp

Post Reply