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Scratch built 45/2A3 SET amp

For cryin out loud Bill! I look away for one minute and POOF. You pull another killer amp outta your :butt1: That looks darling and I bet it sounds even better! You are fortunate to have the CAD and metal skills thats for sure. Makes all the difference in the world! Well when you are bored with it keep me first in line for dibs!!! hee hee hee :D
 
Assembly and wiring are moving along nicely and I think I should be able to do initial power up and burn in this weekend. A cool development for me is that my friend is building his version of this amp with the octal sub-assembly plate and using a Western Electric 717A pentode driver as used in the Yamamoto 45 that BrianB sells. It should be very interesting to hear 2 versions of the same amplifier (both using RCA UX-245’s) with only the driver tube/circuit differing, in one system, back-to-back.

The 417A triode tubes I’m using are on the left, the 717A pentode is on the right.
 

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finally...

Wiring is done short of a few resistors and I'll be ready to power it up on the variac and check voltages tomorrow. I'll do initial testing and burn-in with a CBS 5U4GB blackplate rectifier and Raytheon 5842's and ST 45's. This amp has been a long time coming so I'm really looking forward hearing it.
 
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Not running yet Dan, about to leave on a 10 day vacation and just ran out of time. Kind of frustrating seeing it sitting there soooo close...
 
Originally posted by Billfort
A cool development for me is that my friend is building his version of this amp with the octal sub-assembly plate and using a Western Electric 717A pentode driver as used in the Yamamoto 45 that BrianB sells. It should be very interesting to hear 2 versions of the same amplifier (both using RCA UX-245’s) with only the driver tube/circuit differing, in one system, back-to-back.
Click to expand...

I, for one, would be MOST interested in hearing the results of this comparison... ;)
 
Same here. I'll go ahead and say that it'll sound as great as it looks, too. With so much attention to detail being made on its construction, how can it NOT sound good?
 
Dang, that looks nice! How big of a difference did the DC make on the heaters Bill? My 5V TJ meshies do like to hummmmmmmmmmm.
 
Thanks again for the compliments guys, it’s my second effort at this DIY stuff and it’s been pretty satisfying so far, sure hope the lump sounds ok!

Thatch, I have no plans to go near dc heating on this amp but with the 300B amps, I find it a necessary evil. After building the Schottky bridge>CRC filtered rectifier board I was happy to hear the hum gone but the sound was a little dried out. After playing around with the component mix though I was able to get the balance back where I like it – especially in the midrange. I ended up with a different 6SN7 driver tube (Brimar CV1988), replacing the plastic coupling caps (Multicap RTX) with AudioNote PIO’s, adding a choke (CLC) to the dc filtering and sticking with my favorite 300B for midrange – the WE. I really would have liked to stay with ac heating but it takes a builder with WAY more skill than I posses at this point to get a quiet ac heated amp with 5v 300B tubes. Maybe I’m just being too damn picky about the hum but for some reason it just gets under my skin.
 
so it works...

Ok, I’m trying not to be too excited, it’s only been burning for a few hours, I know the sound will change over the next while and I haven’t used my good tubes yet but man, does this amp sound nice so far. This is my first taste of the 45 tube at home and I think I’m in love!

I only made 1 or 2 stupid, easily fixable mistakes with this amp and I suppose I learned something about layout and grounding from my first project because this one is dead quiet, no need to think about DC heaters here. Voltages are all good but I might want to reduce heater juice a touch – the 417 driver is 6.6v and the 45 2.7v – within 10% but I might want to be picky with expensive old tubes. This is sort of a necessary evil I suppose in Canada where the wall voltage seems a little higher than in the US and the James PT is wound for 115v.

Right off the bat, I like what I hear with this thing. Surprisingly to me, it does a better job in the bass than my 300B amps and isn’t too far behind in the midrange, treble is a touch softer but this seems to be imporving by the hour. The soundspace this amp projects with a good LP or SACD is pretty amazing and I found myself forgetting about the ‘sound’ and just plowing through the record rack to just listen to the music. It’s too early for me to say for sure but it really looks like the <2w output of the 45 is adequate with my 100db efficient Altecs, I really was expecting to be disappointed here but so far so good.

I’m happy and can’t turn the damn thing off; there are so many LP’s I have to listen to again. If things get even better with some burn in and tube rolling…damn, I love this hobby sometimes.
 
Well, Bill I suppose you thought I was nuts

I apologize that I never posted about your latest! What can I say, in a word - awesome! Even nicer than your 300b amp. And what can I say about your reaction to the 45. It didn't take me very long to realize that was it! It's just the truth, and even if it isn't where it may deviate is so beguiling foregiveness is EZ. You say you haven't played around much with tubes yet? Wow, just think it only gets better? What 45's are you using? Remember that the EML's are almost like hearing 45's for the 1st time, all over again.

MikE
 
Thanks Mike and yes, the 45 just might be something special and where I want to stay. I'm using a matched pair of healthy Raytheon 45's now but have a pair of RCA UX-245 globes to try. For drivers I'm using Raytheon 5842's but have NOS pairs of Northern and Western Electric 417A's for later, rectifier is a CBS 5U4GB blackplate and I have a National Union 5U4G to try.

I think I pretty much have the 417 field covered but I'll start rounding up some rectifiers to roll, it's nice to only need 1 in this amp; a lot easier to find (and afford) singles.

As far as EML's go, well, I know you love em and they sure seem to be considered the best by some but I have some reservations as we've discussed. Maybe you should pack em in your overnight bag and make a trip to Toronto for a listen to my system with them, may convince me to break the bank and order a pair :) .
 
I’ve given the amp some time to settle in, moved up to my better tubes (RCA UX-245’s, WE 417A and National Union rectifier) and did the tweeky stuff like putting the Herbie tube dampeners on the 417’s and using the Yamamoto ebony feet from BrianB. Speaker wiring is vintage WE thin ga copper in a 4 conductor Litz braid from ThatchEar (nice stuff Thatch!) and IC’s are Final labs cotton covered copper to the Counterpoint pre-amp.

I am very happy with this amp and really don’t think I’ll touch a thing on it. Maybe it was the break-in time or the tube rolling but the treble has opened up and there’s a better sense of air and space happening now. I still think the 300B amps with WE tubes have the edge in the midrange but it’s probably a kind of euphonic coloration I like, the 45 sounds more natural and balanced. I’m still not really sure that I can live with <2w with the 100db eff. Altecs and the larger room of my new house will be the real test but for now, the power is enough.

The best thing about this amp (or maybe just the 45), is the way it connects you to the music and lets you forget about all the audio stuff. I don’t think I’ve enjoyed sitting back with my wife and digging through the record rack more than I have over the last few weeks. While listening last night, she told me that she likes the system so much now that the 45 and Altecs should really go on the main level of the new house, she says I’ll just have to build more stuff for the dedicated listening room downstairs :) . I like this development, maybe I’ll get to the Edgar horns I always wanted and that 76 pre-amp but you know, when it comes to amps, I’ll build another just like this one.
 
The best thing about this amp (or maybe just the 45), is the way it connects you to the music and lets you forget about all the audio stuff.
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Ditto. You hit on two things that echo what I've said all along. That the 45 is the most natural sounding tube I've witnessed and that it connects me to the music in a singular way. It's always interesting to hear that others share the same opinion. I'm curious what you thought about the bass response? I absolutely feel in love with it! And that quality would shift with the different 45 types. Great news about the honey warming up to 45! Keep the reports coming! MikE
 
717A and 45's

Bill,
I know your amp has to be great sounding. I love my Yamamoto A-08 with 45;s and 717A's and they power up my Edgarhorns rather nicely with a authoritive sound singature that belies the little 2 watt per chnl power levels.

My biggest problem is the room size I have in my house, 12' x 16' limits the real potential of the Edgarhorns.

I am curious to hear more about your amp since you should have more "burn-in" time on it now!!

Great looking amp:D

Ron
 
I finally changed something...

Enough has changed in my system since I first started using this amp that I decided I should experiment a little.

The new room is bigger, better balanced and has way less 1 note bass ‘boom’ which seems to have given everything a somewhat lighter balance. I am also experimenting with a new crossover design for my Altecs that smoothens out the midrange a little and extends treble a touch through the use of a compensation circuit on the horn. It seems to work as intended but it sometimes seems a little too ‘polite’.

I decided to bypass the level pots in the amp as these where intended to act as attenuators in a bi-amp configuration and I’m not there yet. In went some R470 Tantalum grid stopper resistors to bypass the level attenuation circuit. This provided too much gain, increased noticeable hum and sounded a bit ‘shouty’ and forward so I replaced the Tantalum with a Riken 1.2k resistor and this was more like it!

Bass is improved with the system taking on a more controlled and effortless feel. The bass is in better balance with everything else and cleaner now without the 1 note bloat of the old room. There seems to be more detail and a sharper image as well, gone is the overly ‘polite’ balance the new crossover seemed to bring on. I’m back to thinking less than 2w is just fine power wise if I get to use a tube as sweet as the 45.

It continues to amaze me how small changes in circuit, layout or components can transform electronics built with simple, clean circuits like low power tube SET’s. The pot that was bypassed here was a good one – an ALPS BlueVelvet in a Riken shunted configuration – but getting more stuff out of the signal path made a significant improvement. This has really reinforced for me the notion that simple is best.

14745ampshot.jpg
 
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