Small SE 6L6/KT66?

[EFK]

Does such a thing exist? I guess what I'm thinking about is something like a little Champ, @ 5 watts, that can run a single KT66. Can a champ be modded - or say, can a kit build be modded without getting too complicated - to use one of these tubes? I know a lot of guys try out 6L6 in sf and bf champs w/ the Princeton transformers. Any thoughts?

[tubeswell]

The AX84 site has several SE variants which have options for 6L6s or KT66s (or '77s or '88s). In fact I'm looking at building a dual SE KT77 with the AX84 SEL preamp at the mo (as I have a couple of spare large trannies)

[MWJB]

The 125P1B tranny has a 2A 6.3VAC winding, this will easily take 1x12AX7 and 1x6L6/KT66/EL34. The same PT has to cope with more heater current draw in a PR. However with the additional heater & B+ current draw, plate voltage may drop considerably with the KT66 & EL34 at reasonable currents...so benefits in power output will be negligible, that's not to say that you won't like the tone though.

If you're going for 6550/KT88/KT90 then an upgrade PT will definitely be necessary, 3A min? 120mA plus on the B+ winding.

An upgrade OT will be a good idea in all above instances as will 10W cathode resistors for the power tube and 100v bypass caps.

[clintonb]

I have an Electar Tube 10 amp that has one 6L6 and one 12AX7. I bought it years ago when MusicYo were selling them for like $99.

They have gain, volume, treble, mid, and bass controls too. They have chassis mounted tubes and controls that connect to the PCB with ribbon cable, a speaker out jack, standby switch, and a preamp out. It has a crappy 8" speaker.

The Epiphone Galaxie 10 seems very similar to it.

They actually don't sound that good stock, but you could mod them.
I modded mine a lot by removing a lot of stuff from the circuit and making it more like a Champ.

One of the most effective mods is to replace the puny output transformer. The old one was so small, it was mounted inside the chassis. I replaced it with a transformer that came from an old tape player that I found on eBay for $7. I'm sure you could even find a better one that that, but you can't beat $7.

I think it sounds way better plugged into a larger cabinet. But then I notice its low end hum. Or maybe it's the extra bass I get from the replacement transformer that exposes the hum.

The Torres engineering web page has free instructions for building the Tone Frenzy amp which is a high gain SE 6L6 amp. (http://www.torresengineering.com/freplantomak.html).

[mark h]

Are they the Riff Ron mods you've done Clinton? I'm considering buying and moding an Electar. Are there any more mods anyone can suggest? Lots of the mod pages seem to have gone from the internet I suppose because it is no longer in production. I'd like to get more of a Princeton/Champ sound (within practical limitations) rather than aiming for more gain.

[stokes]

The Champ circuit is quite simple to reproduce.It would be fairly easy to build one from scratch instead of a kit.Just get the bigger PT and OT as MWJB has suggested.I built just such an example that my son uses with one of the acts he plays with,it has a KT66 power tube that has a hybrid fixed/cathode bias set-up and a 10" Weber speaker.With another guitar, bass and drummer he has no problem being heard with that amp.In fact the other guitarist has trouble using his Blues Jr in that setting and has me building him a copy of the heftier Champ.It is only about 10 or so watts,but it really kicks ass.

[clintonb]

Are they the Riff Ron mods you've done Clinton? I'm considering buying and moding an Electar. Are there any more mods anyone can suggest? Lots of the mod pages seem to have gone from the internet I suppose because it is no longer in production. I'd like to get more of a Princeton/Champ sound (within practical limitations) rather than aiming for more gain.

Yes, I did a lot of the mods that Riff Ron indicated. His mods lower the gain and remove muddiness. He made it more like a Fender. Later on I just started tearing everything out and making it like a Tweed Champ preamp circuit.

A speaker swap helps, but I think plugging into a speaker cabinet (even a 1x12) sounds way better.

The output transformer sucks. It seems like the bigger the transformer the better. The output transformer for the electar is so small, it is mounted INSIDE the chassis. Replacing it with a bigger one that you mount on the outside of the chassis makes a big difference. I got more highs and lows. More clarity. Weber speakers sell some cheap ones.

However, after changing the output transformer, I could hear a 120Hz hum when plugged into an external speaker cabinet. That apparently is due to inadequate filtering in the power supply. Perhaps it wasn't an issue before because the lows weren't being reproduced so well by a puny output transformer and an 8" internal speaker. I suppose I could remove the hum by using larger capacitors in the power supply.

I wonder how the output transformer of the Electar compares to the Epiphone Valve Jr or the Epiphone Galaxie 10 (which pretty much appears to be the same amp).

To get a sparkly sound at lower volumes, you could add a bright switch like you see on some Fender amps.

It was a fun amp to mod. But I modded it so much that the circuit board traces started coming off.

[tubeswell]

The output transformer for the electar is so small, it is mounted INSIDE the chassis. Replacing it with a bigger one that you mount on the outside of the chassis makes a big difference.

However, after changing the output transformer, I could hear a 120Hz hum when plugged into an external speaker cabinet. That apparently is due to inadequate filtering in the power supply.

Hi Clinton

Just curious. The hum that you are getting might not be due to inadequate filtering. There are several possible sources of hum:

1) Hum from stray EMI from electro-magnetic coupling of the OT with the PT. Did you try mounting the OT iron at 'right angles' to the PT iron? Even moving the OT further away from the PT (if that's possible in your case) might help.

2) Has the 'replacement' OT got steel end covers? When you positioned the new OT on the 'outside' of the chassis you may have exposed it to more EMI from the PT than the old one was getting

3) If the new OT is more sensitive to 120Hz ripple from the power supply, then try increasing the CRC resistor a tad, or maybe put a 50mA HT choke in there instead of a resistor (i.e. convert the CRC filter into a CLC filter) - but if you do this you might want to put in a 470R to 1k5 5W screen grid resistor from the screen supply node to the grid pin of the output tube screen grid, to keep the screen more or less below the plate voltage

[tyru007]

My first build was a BF Champ head and 12" speaker cabinet. I ended up changing to a KT77 recently, which greatly improved the balance of the amp.

I used Hammond 270EX power transformer and 125ESE OT for a max of 15 watts. Currently I'm getting out a little less than 10 watts but very loud with a 12" speaker.

See my thread here.

http://music-electronics-forum.com/t10213/

The amp is built on a AX84 chassis drill plan.