Bedroom Plexi PPIMV

[Littlewyan]

You lucky git! Don't get any of that with smaller bands, it seems now everyone is trying to quieten down. Whenever I play with my band I try to bring the volume up but no one shares my enthusiasm. Especially not the sound man!

[Phil_S]

Let's just say it wasn't so easy to come up with $6 back then. However, the inflation calculator says that is today's equivalent of only $42. They weren't the best seats in the house. It was what we could get when we got around to buying them. The rebuilt MSG had just opened earlier that year. As I recall, it had a capacity of about 20,000 and it was sold out.

[mhartman]

I wouldn't worry about the voltage switch, just do the PPIMV. If you really want to tweak the voltages, go a step further and build in power scaling. I just built one with both and find myself sticking to the PPIMV and not toying with the power scaling too much.

[10thTx]

You can build a 6V6 Plexi and use Dana Hall's VVR. That way you can use 6V6's or 6K6's.

BTW, I think you can get a pretty big sound with 6K6's :
http://www.soundclick.com/player/single ... i&newref=1

AND ................ you can do a octal socket to a noval socket conversion to go to ECL84's for a 3-4 watt push pull power amp also. The SoLow Watt used ECL84's and has a good tone.

You'd have a mini-toggle that switches the power tubes cathode resistor and cap out. I have done this and it works fine, IMO. I was switching between 6V6/6K6 to 6BM8's.

http://el34world.com/Forum/index.php?topic=16786.0

Then with the VVR and a PPIMV you can get everything from 12 watts to 1.2 watts.

Just an idea to consider. with respect, 10thtx

[stephenl]

Bedroom level is 1/4 watt. Even a 1/2 watt is fairly loud.

I think the best approach is to build the PA that you like the sound of and add PowerScaling, VVR, or my favorite - use a BadCat Unleash.

[cbass]

I built a cathode biased pp 6v6 amp with about 250V on the plates it was still pretty freaking loud
Cerinaly louder than a single ended amp I have running the piss out of a 6v6 with about 380V

[Littlewyan]

Hmmm maybe I should stick to a single ended amp, but use a different design. Seen a few with Plexi Pre Amps and they didn't sound too bad. I'm just not sure the single ended sound is for me.

I've already got an attenuator so should be fine, especially with the PPIMV! Thanks for all of your suggestions. A lot of food for thought!

[mhartman]

Hmmm maybe I should stick to a single ended amp, but use a different design. Seen a few with Plexi Pre Amps and they didn't sound too bad. I'm just not sure the single ended sound is for me.

I've already got an attenuator so should be fine, especially with the PPIMV! Thanks for all of your suggestions. A lot of food for thought!

+1 on this. My bedroom level hot-rodded plexi is parallel single ended - very flexible and quiet when I want it to be.

[Phil_S]

I was a real skeptic about PPIMV until I put one into my last build. I'm totally converted. For a loud amp you intend to use in small quarters, it's a "must have."

[Littlewyan]

Yer I agree its a great idea, but I imagine I'll need it turned down pretty low for bedroom use. I'm getting turned onto the 1Watt JTM45 now, as the transformers are only £35 altogether! Only issue I've got is finding a chassis. Going to see if I can get a Hammond Chassis to fit into this head cabinet.

http://www.ampmaker.com/infocentre/thread-32.html

I've attached the schematic that I'd use. C301, C15, C17, C19 all look like they can be omitted as they were probably for keeping the amp stable on a PCB. Don't understand R34 and R32 so took them out and used a 500K Pot for the volume instead. In LTSpice the changes I've made don't appear to have affected the amp at all, except for taking out R34 and R32 but I compensated with the 500K Pot.

[printer2]

I just built a 2W (just a guess) 5E3 using a pair of 6AK6's and a 70V line transformer. Plate voltage about 220-230V. I was going to do a Bassman with it before but never got around to it till this project got my curiosity going.

https://tubeamparchive.com/viewtopic.php?t=25023

Actually thinking about it I could use another 12AX7 and do the Bassman without the presence in this chassis. A bit trickier changing to LTP though.

[printer2]

Might as well point out this guy`s amps.

http://www.bluetone.fi/en/jcm-800-jr/

http://www.bluetone.fi/en/lead-jr/

Almost forgot this one. That would be a no-no on this forum.

http://www.bluetone.fi/en/express-jr/

[Littlewyan]

Never heard of Bluetone before, nice amps though. Wasn't very impressed with their Express Clean Sound though, because it wasn't clean!

Your amp looks good, where did you get that chassis? Quite impressed you fitted everything in it. Thats the difficult part with these small amps, cramming it in and making it stable! Also wish I could build a cab like yours but I don't even have a real workbench!

[printer2]

Never heard of Bluetone before, nice amps though. Wasn't very impressed with their Express Clean Sound though, because it wasn't clean!

Your amp looks good, where did you get that chassis? Quite impressed you fitted everything in it. Thats the difficult part with these small amps, cramming it in and making it stable! Also wish I could build a cab like yours but I don't even have a real workbench!

The guy who runs Bluetone has been on various amp building forums, I think named harryk, learning and helping others the same. Up until a while ago he even kept schematics of his amps for anyone to download.

The chassis is a piece of aluminum that I bent up before for a head, decided to use it for this amp so I cut it down and then bent the bottom two bends in my vice. Clamped it between two pieces of steel and then used a hammer and a block of wood to bend it. Not too hard to do with aluminum, but you do need a bench.

The board was just laid out starting from the input to output, just started stuffing parts in. You are right about the stable part, while the board looks crowded I did space the signal carrying components out but the filter caps and resistors filled the empty spaces. Without them it is easier to see how I kept things apart.

I rigged up a jig for doing box joints and since I had it set up I made a whole slew of cabinets that I am finally getting to fill. I`ll throw on some more pictures of the amp being built and a few on my building methods in my thread, do not want to hijack yours. I agree with you about the clean recording. One thing I wish people would do with their vids is to show the range you can get out of the amp. A number of Express ones shows the clean and dirty, almost like idle and full throttle.

[gingertube]

Unless you go for one of those PP 12AU7 Output stage amps then obtaining "bedroom" levels are going to be a problem unless you use VVR or Powerscaling.

You can do little amps with any of the triode pentode tubes.

There are 3 Options in the Triode / Pentode Tubes

No New Production - NOS Only
6GW8 / ECL86 - The triode is a 12AX7 triode, the power pentode is a high gm pentode like a lower rated EL84

If you do not like EL84, EL34/6CA7, KT88 high gm output tube sound then you might be better off with

EITHER:
6DX8 / ECL84

6BM8 / ECL82

Both available in NOS or Current Production.
The triodes in these are lower mu but from a final sound point of view it is more significant that the power pentodes are lower gm more like the 6L6, 5881, 6V6. If you like that sound better then these are the go.

There was apparantly an ECL83 too but thay are now rare as Rockin Horse Manure.

I have not heard the current production Russian 6DX8 (ECL84) in a guitar amp but have heard them in a a little HiFi Amp and they were seriously good in that.

Cheers,
Ian