Military projector amp - last edited 9/26/22 - layout help needed

[JMPGuitars]

Looks like the 100uf cap, that is suggested to change to 1000 or 2200, is labeled as a 25v cap. I'll keep the other caps within a lower range with frequency response in mind.

That's correct, the power tube cathode cap is higher voltage, but still not super high. If it had 25V, you can go between 25 to 50V depending on what's available with little concern for size. The 2200uF caps I use in my EL84 powered amps are rate 40V, and the average voltage there is about 12VDC.

Thanks,
Josh

[zaphod_phil]

@yello,

As I was studying the Bell & Howell amplifier schematic, it occurred to me that you have most of the parts there for a 10W version of a F***er Tweed Deluxe, either the 5D3 or 5E3 variant. So for a little extra challenge and some awesome sounds, I recommend converting one of your B&H amps to a Tweed Deluxe. I tend to think of the 5E3 as Leo's fire-breathing equivalent of Marshall's 18W - https://ampwares.com/schematics/deluxe_5e3.pdf

While the 5E3 is the most popular of the two, personally, I think the 5D3, with its paraphase PI, has the sweeter tone http://www.thetubestore.com/lib/thetube ... ematic.pdf
For support, our companion site ppwatt.com has a 5E3 mods forum - http://www.ppwatt.com/5e3-mods

Also lots of good information on https://robrobinette.com/5e3_Modifications.htm

[Bieworm]

@yello,

As I was studying the Bell & Howell amplifier schematic, it occurred to me that you have most of the parts there for a 10W version of a F***er Tweed Deluxe, either the 5D3 or 5E3 variant. So for a little extra challenge and some awesome sounds, I recommend converting one of your B&H amps to a Tweed Deluxe. I tend to think of the 5E3 as Leo's fire-breathing equivalent of Marshall's 18W - https://ampwares.com/schematics/deluxe_5e3.pdf

While the 5E3 is the most popular of the two, personally, I think the 5D3, with its paraphase PI, has the sweeter tone http://www.thetubestore.com/lib/thetube ... ematic.pdf
For support, our companion site ppwatt.com has a 5E3 mods forum - http://www.ppwatt.com/5e3-mods

Also lots of good information on https://robrobinette.com/5e3_Modifications.htm

I thought the 6G3 was the fire-breathing monster Leo created!?

[zaphod_phil]

No, the 6G3 Brown Deluxe is a very tamed-down version, thanks to its negative feedback. It's a much later product than the 5D3/5E3 Tweed Deluxes and Leo's amp designs got cleaner and cleaner in each successive generation.

Further discussion on this topic will probably best be continued on our companion site, www.ppwatt.com

[zaphod_phil]

Looks like the 100uf cap, that is suggested to change to 1000 or 2200, is labeled as a 25v cap. I'll keep the other caps within a lower range with frequency response in mind.

That's correct, the power tube cathode cap is higher voltage, but still not super high. If it had 25V, you can go between 25 to 50V depending on what's available with little concern for size. The 2200uF caps I use in my EL84 powered amps are rated 40V, and the average voltage there is about 12VDC.

Thanks,
Josh

Just keep in mind that in cathode-biased amplifiers, the cathode voltage will swing upward on signal envelope peaks. So I tend to use higher voltage rated caps on the power tube cathodes.

[Bieworm]

Looks like the 100uf cap, that is suggested to change to 1000 or 2200, is labeled as a 25v cap. I'll keep the other caps within a lower range with frequency response in mind.

That's correct, the power tube cathode cap is higher voltage, but still not super high. If it had 25V, you can go between 25 to 50V depending on what's available with little concern for size. The 2200uF caps I use in my EL84 powered amps are rated 40V, and the average voltage there is about 12VDC.

Thanks,
Josh

Just keep in mind that in cathode-biased amplifiers, the cathode voltage will swing upward on signal envelope peaks. So I tend to use higher voltage rated caps on the power tube cathodes.

I use the 63V big barrels mostly

[yello]

https://youtube.com/shorts/n6e3QpzRGJA?feature=share


Same amp type, different amp, different problem.

There is a static on the notes. It is different than the overworked clubby speaker issue of the other one. Any idea what might typically cause this?

I have eliminated the speaker, tubes, guitar, or cable as the cause, it’s somewhere in the circuit.

I have replaced the power filter caps, but not yet the 100v 25uf Mallory cap. I also replaced a coupling cap that was very microphonic. The static issue did not change before or after that cap.

Any ideas?

[Bieworm]

https://youtube.com/shorts/n6e3QpzRGJA?feature=share


Same amp type, different amp, different problem.

There is a static on the notes. It is different than the overworked clubby speaker issue of the other one. Any idea what might typically cause this?

I have eliminated the speaker, tubes, guitar, or cable as the cause, it’s somewhere in the circuit.

I have replaced the power filter caps, but not yet the 100v 25uf Mallory cap. I also replaced a coupling cap that was very microphonic. The static issue did not change before or after that cap.

Any ideas?

If that is signal related you'll be better off with a scope . Starting at the input.

[yello]

Unfortunately I don't have a scope.

[Bieworm]

Unfortunately I don't have a scope.

That makes it harder. The only option is to start replacing parts one by one.. or buya scope. A Siglent isn't expensive

[yello]

Is there a certain model Siglent you recommend?

[Bieworm]

I have the 1102 CML

[JMPGuitars]

Is there a certain model Siglent you recommend?

That depends on your budget. Bieworm has the SDS1102CML+ which is $299. The SDS1104X-E is $499, and a great scope. I use the SDS2104X+ (upgraded to SDS2504X+).

[yello]

While I consider the scope purchase, and potentially wait for it to arrive, are there particular components to consider replacing first like disc capacitors (I already replaced one that was microphonic), or particular parts of the circuit to start exploring in?

[Bieworm]

Don't start replacing stuff randomly. You might create other problems along the way.
Try the non destructive way first

You could try eliminating what's good or bad when you take another same amp.
Take the power tubes out of this one.. make a long alligator clip wire and clip it between the same points in both amps. Always the grid input of a preamp triode.. starting from V1
This is what I did at some point when I couldn't find the problem in an amp. Watch out.. it's noisy too with the long antenna wire
But you should get the scope! You're not planning on stopping the amp prodding business anytime soon me guesses

Still recommended as plan A, the scoping. That will definitely give you more insights you will benefit from in the future

[JMPGuitars]

As always, step 1 is knowing and understanding your VOLTAGES.

You need to take voltages in the amp in question, and I assume you have a few more nearly identical amps you can take voltages from to make a comparison.

That kind of static could have a few causes, and knowing what's going on with your voltages may help you determine that.

Bieworm is correct, randomly replacing items could cause entirely new problems. Start with voltages, voltages, and more voltages. And be safe in the process.

[yello]

Anyone have some good online resources for learning how to safely take voltage readings?

[JMPGuitars]

Anyone have some good online resources for learning how to safely take voltage readings?

I'm sure Bieworm or somebody else could supply you with some useful links, but in the meantime, here's some basics.

1. Safety first. every warning about working on tube amps on the entire internet.
2. Make sure your amp is properly grounded. If it's not grounded, replace the power cable/jack with a properly grounded connection.
3. Seriously, don't touch the amp if it isn't grounded properly.
4. Using a good quality DMM (Digital MutliMeter), connect the ground probe to ground with whatever clamping attachment (alligator etc.) came with it.
5. Keep one arm in your pocket, or behind your back. Make sure you handle the probe safely, only touch ONE spot at a time, don't slip and short anything out.
6. Set the DMM to the correct voltage type (AC or DC).

Being careful, and taking your time, test your wall voltage at the amp's inlet, then work through the rest of your AC voltages at the PT including the heaters.

Set the DMM to DC and start measuring your DC voltages starting from the B+ line, and get all the relevant tube voltages (cathode, screen, anode). For reference, look at one of my voltage test charts in the downloads section to get an idea of what we look at.

Also, BE CAREFUL.

Thanks,
Josh

[yello]

Great advice, the chart will be handy to guide me.

I turned the amp on now to check out the sound again and it wouldn’t turn on. Fuse was blown. Opened up the amp and noticed that R210, a 1meg feedback resistor for v201 was cracked.

Possible that part was failing and causing the static, then it finally gave up and blew the fuse?

[Bieworm]

It's possible.. you know what to do next now