6L6SE guitar amp project...

Found a design problem after running it a while,,, seems on the mule the diodes were suspended across a pair of tag strips, lots of air circulating... On the chassis turret board they lay on the board, and apparently overheated, and shorted... Got it running again with the same type diodes, clipped in... Think I'll re do the turret board mounting, and raise them above it, also install higher V diodes and an inrush protector to allow some start up protection....
Its been running a couple hours now, at least it still sounds good, and is quiet!!!! Rebuilt a VC pot got it installed also, so we're still going forward!

Any one in the area know of a radio shop/store etc to pick up a pair of diodes?? Seems closest open Radio Shack is in Lancaster Cty hour+ each way... Hate to bug Digi for them!!
 
Our two RS stores closed a few years ago. The last repair shop only does warranty work on flat screen TV's and installs security equipment now. I used to get parts from a custom car audio shop, but after many years the owner retired and closed up his shop. It's either order online or drive for an hour one way to Fry's.
 
Our two RS stores closed a few years ago. The last repair shop only does warranty work on flat screen TV's and installs security equipment now. I used to get parts from a custom car audio shop, but after many years the owner retired and closed up his shop. It's either order online or drive for an hour one way to Fry's.

Yep same here, too bad its not hamfest season! The local one was a mile away,,, and 2-3 more within 5mi,,, Guess we didn't support em enough!!!
I build a "daughter board" to raise the diodes above the turret board,, just sealed it and waiting for it to dry...
I originally planned to use a tube rectifier, more in line with a Champ, but it would take up more real estate in the chassis, and would move the PS closer to the signal circuits... Probably needed to build a bigger chassis then would fit in the 5F1 box...
So I tried SS,,, nothing I really like about it so far! I have way more support parts for tubes,,, and I think the standby switch is more for letting the tubes heat up and taming the inrush, than keeping it warm between sets!!!! I do have a 5V winding on this PT, if it really bothers me down the road... Don't remember if your PT has 5V, but with that big chassis, I would try it!!!!
 
It does have the 5v winding. I thought about it. The chassis is big enough. The design was meant to use diodes but I did see a few builds where people used tube rectifiers. People have been using this amp design for a few years now and I haven't seen anyone having problems with the 1kv 1 amp diodes yet. But your voltage coming off the secondary is a lot higher. Did you wind up adding a thermistor?
 
I just put a couple CL90 on the Digi order... I also ordered bigger diodes,,, This should keep them elevated a bit... Figure I'll wait til I get the bigger ones rather than take it apart twice,,, I can run the amp fine with the diodes I have,, so I'll keep running it on leads and tuning it, see if any other gremlins pop up!
 

Attachments

  • P8110209.JPG
    P8110209.JPG
    82.5 KB · Views: 18
Been a while gathering the last parts, this is its final "look" in the black utility case,,, as I built the chassis to fit in the Champ 5F1 cabinet... This black box is just to hold the tubes vertical if I want to use it... Ended up using the standby switch to start it, so the caps wouldn't surge over spec... Works better than I expected... Still playing with some Tone control mods for it, but its OK as is,,, more Bass than the average Champ, and can get loud!!! Maybe Paul will post a pic of the one he built when the case is done...
 

Attachments

  • P8290223.JPG
    P8290223.JPG
    83.5 KB · Views: 22
  • P8290224.JPG
    P8290224.JPG
    79 KB · Views: 22
Keep me posted on the tone tweaks! I'm curious as to what you find.
I saw John's thread and it looked like a fun project. Plus my son has been wanting a lower watt amp. I haven't stuffed mine in a cabinet yet. Waiting on my son to bring an old combo case to mod.
20190103_134527.jpg 20190108_104115.jpg 20190115_125939.jpg 20190115_140722.jpg 20190122_090131.jpg
 
Using a thermistor without a standby switch worked well for me. 400v peak, then settled down to around 360. But my trany was a lower voltage than John's.
 
Glad ya joined in!!! Using the standby switch, B+ starts at just around 350VDC when tubes are hot (30-45 seconds)...
Here's a couple I was looking at,,, http://monster.partyhat.co/article/amplifier-tone-stacks/#one-knob-tone-controls

I used the Tweed Princeton in my 5F1 clone,,, Its OK, I'm sure there are better ones out there, but it keeps the Champ tone... Moonlight is interesting as it has a bypass switch (push-pull on the tone pot),,, I'm looking for a one-knob control, with more Treble than this amp design has, as the control on this one is Treble cut,,, I think this amp is a little Bass heavy,,, my impression is it sounds better with a humbucker than single PUPS...

There are the designers tone stack mods for this amp out there, but I can't seem to find where I saw them now!!!!!
Also,, I like the sound of it with the 5881 better than 6L6GC,,, but I used 2x 6SF5 preamp tubes, and a different OPT then you, so YMMV!!!!
 
I popped a 5881 in and it sounded better also. You may he right too about the OPT you used. But still, not bad for a pile of leftover parts. :biggrin: since I had the shielded socket and a pile of 12ax7's I went the easy route. I will admit the cheap $6 no name 6L6 I tried sounded pretty good too. The 5881 had a slightly better top end. These small guitar amps are fun little projects.
 
Good to hear,,, I have an NOS pair of RCA 6L6GC black plates a buddy gave me,,, hate to break em up to use here tho!!! Maybe a 6L6PP amp in the future!? I don't have spare 12AX7s, just use em in commercial amps,,, I think octals are easier to work with, bigger sockets and less pins for these old eyes!
Are you going to use your sons old amp cab, or the Poplar?
 
Good to hear,,, I have an NOS pair of RCA 6L6GC black plates a buddy gave me,,, hate to break em up to use here tho!!! Maybe a 6L6PP amp in the future!? I don't have spare 12AX7s, just use em in commercial amps,,, I think octals are easier to work with, bigger sockets and less pins for these old eyes!
Are you going to use your sons old amp cab, or the Poplar?
Not sure yet. I have to look at the empty combo he brings. If it's easy to mod I'll use it. I almost used a 6SL7. But then I found the shielded 9 pin socket. I'm hoping the amp can fit his cabinet horizontally. It shouldn't be a problem using 5881's that way from what I've been told and read.
 
I just noticed R17(47K) on the schem is not on the chassis layout... I'll have to jump that out and see what difference it makes... Did you use R17 in your amp?
 
I just noticed R17(47K) on the schem is not on the chassis layout... I'll have to jump that out and see what difference it makes... Did you use R17 in your amp?
Yes I used it. The chassis layout was an earlier version than the drawing. R17 was part of the update to the tone control. I went by the drawing. The layout also shows the one end of the pot connected to the wiper. The schematic has that end left unconnected.
 
Yeah,,, I saw that jumper on the pot,,, I jumped that 47K out and it didn't seem to change anything... That's when I noticed the Tone ckt problem... The schem is version 3, layout is one, IIRC...
 
It's getting warmer now and I was able to get the clear coat on the the head amp cabinet. This was a fun little project. A big thanks to John for posting this thread!
20190319_141846.jpg 20190319_141827.jpg 20190319_141812.jpg
 
Update...
OK,,, this build really wasn't done, after I talked to Paul about how his basically stock version came out!!! The OPT I used wasn't good enough for the task,,, so I put the amp on the shelf, until yesterday, after I got the UTC txs... They are definitely full range, even as PA duty, and a PS resistor change brings the B+ thru the amp right to specs...
OPTs are the most important part of an audio/git amp,,, I just finally proved it to myself!!!! This tx may be overkill for this project, but for the money, I will sacrifice one of them to this build!!!!!

Here it is idling, waiting patiently for some input!!!!
 

Attachments

  • P2140064.JPG
    P2140064.JPG
    82.5 KB · Views: 23
Back
Top Bottom