Been trying out different power tubes in my express clone. I've come to the conclusion that tube selection is much more critical in an express based amp than in say a Marshall based design. So far my favorite power tubes are an NOS set of GT labelled Siemans EL34's followed by a set of Amperex Globe logo labelled Mullards. I tried a set of GE big bottle 6CA7's that are very thin sounding and a set of new production Svetlana's (Sovtek) that have a problem. With the Svets on the leading edge of certain notes there is a crackle. It is most noticeable on the g-string between the 3rd and 12th frets. It doesn't happen with ANY other tubes. I have also tried 6V6's. They are FAR more civilized in this amp. I haven't finished testing all my 6V6's yet so I can't pick a fav yet BUT they are all pretty good so far. I still like the EL34's better though. They are more unruly but the payoff is better in the end. Pre-amp tubes are V1-smooth plate Telefunken 12AX7, V2-IEC/Mullard 12AX7 V3-IEC/Mullard 12AX7.
I used shielded cable from the input jack to V1 and from the center lug of the VOL pot to V1. I put silicon sealant on the back of the bright switch to "glue" the caps to the back of the switch to stop parasitic oscillation. Other than that I didn't alter anything. I used the A1a schem and the "Kelly 90" schem to build it.
I biased it based on what KF says in "The Trainwreck Pages" which states to bias an Express put -30vdc on pin 5 of the output tubes sockets.
The amp is definately growing on me. I wasn't sure if I liked it the first few times I plugged into it but I have been dialing it in and I think it's a lot better than I had anticipated. I would like a bit more bass though.
Hi Heebgb,
The build looks great!!! Have you tried a Mullard in v1? I find the amp to be more aggressive with a sheild logo 12ax7 for v1.
For power tubes, I found the 6ca7's to be thin also.I wound up with some mazda labeled 34's.........they look like seamans to me.......
I will have to try the sealent on the bright switch.........do you think it made a difference? I have sheilded wire there from the center of the switch to the center lug of the volume control.
Again looks great !!!!!!!!
Chris Gondoli
Heebgb,
The amp looks nice! I have a mullard in the first preamp socket and it sounds great. I've tried all the other brands and the mullard wins hands down!
First, like your amp, my amp is not nearly as wild and out of control with 6V6 tubes. It's also a lot less loud, and has less low end. But I like them a lot.
Also, I have a couple NOS Mullard series 10M 12AX7 tubes that I picked up at a flee market a couple years ago. They sound good and are not microphonic. However, I felt the amp had more midrange projection (in a good way) with a lower gain Ruby for V1 and sovteck LPS tubes for the other positions. I paid the extra price to have them matched.
Of course, maybe I'm just fooling myself because I don't have that great stash of NOS tubes of yours!
I have a bunch of Mullards. The IEC's are pulls but I have two NOS in Mullard boxes shield logo AX7's. I got them from Watford valve at the Dallas guitar show last year for $65 each. I only wish I had nore money with me at the time. The Mullards are a favorite for sure. I also really like the Smooth Plate Tele's and Amperex globe logo's. The RFT's are pretty good too. They are all good and certain amps like different brands in different positions. I haven't done the pre-amp yet. The 3 tubes in there are just a baseline for doing the power tubes first. Then I will do the pre-amp.
I definately like the Siemans 34's the best. I haven't finished the 6V6's yet but the RCA brown base JAN's are my favs so far. I must say I have a pair of Sovtek 6V6GT's that I do like in this amp. They are probably 10 years old at this point but relatively unused. I like the way they roll off some of the high end. The amp has a ton of high end. Still the RCA's rise to the top of the 6V6 group. None of the 6V6's were bad BTW. not like the 34's. The GE 6CA7's were not good in this amp.
The Silicone definately helped an oscillation problem with the bright switch caps. I soldered the caps directly to the mini toggle (DPDT). During debug I was poking around with a chopstick and had to bend the two caps down to get to a wire I wanted to poke. When I put my finger on the caps and held them down the oscillation stopped. I used ceramic disc caps BTW. I used clear silicone sealant but you could probably use a hot glue gun (AllynMey's idea) and or some kind of 5 minute epoxy. Now I only get problems when I get close to the speaker cab or the bare chassis.
Also, the amp is much more playable, as far as uncontrollable feedback is concerned, when you have 6V6's in it. At full volume with 34's in it....I think it just oscillates the whole room. I have been dialing it in and like it very much with the volume set at about 9 or 10 O'clock. That's still a lot of gain but the amp is very responsive there and has more than enough gain for me. I must say the more I play it the more I like it. Definately not a beginners build. I am glad I have a bunch of different amp builds under my belt before attempting this one.
Nice looking build. For more bass you should try substituting a .0047 for the .0022 coupling cap between the 2nd and 3rd stages. Did you make the chassis yourself. Just curious which transformers you used.
Thanks! Yes I did bend up the chassis myself. I also made one for Allynmey. I got my tranny's from Moose on this board. They are Heyboers I believe. I am using the 6600 ohm tap. I haven't had the chance to try the 5200 ohm yet but it's on the project board if you know what I mean.
The Ceriatone chassis looks good. I may do another build based on that chassis.
Thanks! Yes I did bend up the chassis myself. I also made one for Allynmey. I got my tranny's from Moose on this board. They are Heyboers I believe. I am using the 6600 ohm tap. I haven't had the chance to try the 5200 ohm yet but it's on the project board if you know what I mean.
The Ceriatone chassis looks good. I may do another build based on that chassis.
Greg
Hi Greg,
You should realy try the the 5200 taps.......I think in my build I lost a little clean head room but the overdrive was very nice!!!!
By the way any thoughts on another amp fest down your way any time soon?
Thanks!
Chris
Funny you should ask that. I am planning another tentatively for December 10th. It's not definate YET. I will post details when I get them finalized.
On another note (This just got confirmed yesterday) This friday I will have a small gathering of the local crew (everyone is invited though it's short notice) and one of my closer buddies takes guitar lessons from a guy named Nat Janoff. Nat is a MONSTER player (you should look him up on the web). Anyway Nat is the proud owner of a real Express. Nat will be attending this friday night with his Express. I will be comparing my newly completed clone to the real deal. Obviously I don't expect my amp to keep up but I am hoping to get some insight into how to improve my amp.
I WILL take pics and post them here. I hope he doesn't have to cancel or something.
I am a big fan of smooth-plate Tele ECC83/12AX7 tubes as well. For some sounds, they just work better than Mullards. Probably not in a Trainwreck though. I was also going to say "Nice pair of Sylvania 6V6s!" but it sounds like you prefer the RCAs.
I find the Tele's work well in almost all applications. Sometimes I do prefer something else but as a baseline the tele is always a great starting point.
The Sylvania's are great for sure but with all the gain in this amp I prefer something a little less gainy.
I can't wait to hear the real deal on Friday night!!
Glad you liked the bass boost. We really should experiment abit more with values for that cap. Its really nice when one value change makes such a difference. I'm looking forward to your post regarding tonight as well.
I have a mullard in the first preamp socket and it sounds great. I've tried all the other brands and the mullard wins hands down!
