Home Brew SET Tube Amp # 45 High Power?? 1.75 watts

[kcline]

My good tech friend is back in town after moving 5 hrs away in the extreme southern mts. of NC 9 miles north of GA line. Last fall when I got my Cornwalls, I asked if I could use this amp to hear what 1.75 watts sound like. He has not had a system setup in 5 years, always comes to my place to listen to my setups which he restored all of my tube gear. He is building new work shops at his new home for Electronics, Metal working and Wood working, already has Auto work shop set up, my friend does do it all. Please see pictures, amp has not been powered in 6 years so I will bring it up later after I connect it up. All you see outside of the tubes, those came from me, he bought at various Hamfests over the last 50 + years.

 

[Dave451]

Looks like a nice piece of work. Big output iron (look like Scott transformers; maybe Dynaco?) and look at all those chokes! Must have a smooth power supply.

 

[trainbuftony]

I agree, it looks well built. I would tend to doubt the transformers came from HH Scott, or Dynaco, as all of their designs were push pull. I dont know where they did come from, cant help there. Push pull transformers Do not work in single ended amps, they aren't interchangeable...

 

[Dave451]

Yep--they do look like them, though!

 

[kcline]

Today I bought amp up with one of my variacs, AC voltage today was 118, wide open on the variac was also 118 no boost in this variac. Amp is in my Analog room #1 Fisher 400-C pre, Mac. MR-78 and of course Pro-Ject TT. I let amp warm up with the tuner playing NPR, needed more gain from pre, around 11:00 instead of around 9:00 with my normal amp Heathkit W-3AM Williamson pair. Sound was a little darker so I checked the tone controls and mover them both to str. up instead of the treble cut I was using with my other amps. 1.75 watts does play well with the Doc Watson and the Leonard Cohen that I played, not sure how heavy rock will work out. Next time I will plug directly into AC, if you notice the small brd. at the top of the photo is a AC line filter so it does not need the bucking transformer that I use with my other amps. After my next session I will start tube swapping, right now there is a pair of #76 in adapters to use in place of 6J5 or 6C5 tubes. In the rectifier socket is a 5AR4 Mullard 4 notch any rectifier with same pinout will work, I will leave that tube in place for now, then I have many #45 tubes ST and globe to try out. Amp does have distortion pots to fine tune output need scope to mess with those so I will leave those alone for now.

 

[kcline]

Been playing SET amp early today it really does sound nice after playing more folk stuff like Phil Ochs Leon Redbone , Put on Frank Zappa still sounded good but needed more punch for Frank to sound his best. Phone call came so I powered off, came back in 10 mins. and placed a pair of globe 45s in amp 1st pair after about 30 secs. tube on left became gassy, pulsing in time with music, so after another 10 mins power down, I placed a pair of RCA UX-245,s in, these both tested at 1200 on my TV-10 which is just above the min. They played very well sound stage seemed a little wider and these had more high end then NU ST-45,s that came with amp. They played noise free. I had a customer that I sold quite a few sets of globe 45,s to who told me that if they do not test strong which on my TV-10 is above like 1800 or so they will be noisy, these were not I do not know what circuit his amp had but these played great. I will do more testing next I will try a pair that test weak and see how they sound

 

[kcline]

Played SET amp yesterday for 6 HRS. Placed back in the ST-45,s that came with amp. Amp was "fine tuned" with those tubes in place. Removed #76 tubes, replaced with 6J5-G Syl. Acoustic, Bluegrass, Folk, Country and 1960,s Moog LP!! are some the music that I played. After what seems to be a long warm up over 30 mins amp just opens up, large soundstage with depth on well recorded LP,s Still very pleasant lain back sound on lesser LP,s due to worn LP,s grooves. Nothing played sound harsh, all was laid back, very addictive sound, I now know why SET is so popular. Now the down side, with rock music, there is just not enough power for correct play back for me, needs another watt or two. Acoustic bass is also a little soft, On the LP set "Will the Circle be Unbroken" UAS 9801 3 LP set the late great bassist Junior Huskey is playing bass on most cuts, the slap of his bass is muted compared to my normal amps, its there but it sounds like the bass is further back in the mix. The Moog LP that was so great is " Moog Groove" Stereo LS-86070 from the 1960,s the songs are just covers but the first cut "Aquarius", Wow, the sound is like a bubble that grows out around and above and behind the speakers with the sound going back and forth between the speakers, this I did notice but not as much with my other amps. This is also a VG+ pressing very nice for used 1960,s LP. Next is long session with Globe 45 tubes, this is a little unfair as I have no way to "fine tune" this set of 45,s

 

[kcline]

Yesterday I installed the RCA UX-245 pair. These were tested with my US Military TV-10 tester. Min is 1140 both of these tested at 1200 so close to min. When I was a dealer many customers told me only NOS or strong testing, i.e. around1800 or better on Hickok type testers, would work well in SET amps now what amps I do not know, but in this amp this pair of 45,s played very well, as good as the NU ST-45 that came with amp? A little different more "airy" then ST-45 and they seem to warm up faster then the ST-45,s. Next a stronger pair of Globe 45,s I have a few more.

 

[kcline]

Today played pair of 45,s that tested above 1700, to me played the same as pair that tested close to min. Up next is pair that test weak around 900 to 1000.

 

[kcline]

Thursday I installed a pair of UX-245 RCA, these tested weak 1000 min. good is 1140 on my US Military TV-10 tester. Before I get to the results of this test lets talk about # 45 tubes. For years I did tube related talks at the CC-AWA Radio meet in Charlotte NC. I am a past member of the now defunct TCA, there is still a website. I have demonstrated at talks that tested weak 45s will still work and in lots of push pull circuits from mostly 1929-1930 radio years. I told all radio collectors not to toss weak 45s but try them in their sets, they may still work. I had a American-Bosch set coffin style cab that set on top of speaker cab, speaker at bottom kind of a low boy. This played with 45s that tested at 600 very weak tubes. OK now back to audio. The tested at 1000 pair played well, they were not noisy, while I let them warmup I had NPR on, it sounded like normal for this amp. no different then the good tested set. Played some Leonard Cohen, Bird on the Wire was one, playing just like on the good set. Now these must have less output? I have no way to test power output, when my tech buddie gets set backup maybe we can to some power testing.

 

[kcline]

My current thoughts on this SET amp. Great separation and soundstage depth, vocals in jazz, folk other acoustic types very nice, amp is very easy to listen to and big plus in hot weather it runs very cool, I can touch output tubes even after playing for hours. Downside, just not enough power compresses transients even with vol. level set at that magic spot, harder playing music just does not sound right good sound but compressed. Not the amp for R&R Frank Zappa bass lines seemed to be deeper in mix with less slap, as most bass was however acoustic jazz bass was very good. Still like amp a lot, hope to be able to keep, will see. Now this ARC St-70C3 amp is in place: Running it using the " Line Voltage Corrector" a buck or boost variac at 114 drawing 1.4 amps, after warm up amp needs much less input NPR plays fine at 9:00 LPs right around 12:00 which is a good spot on this org. control. Less separation then SET amp, soundstage not as wide but almost as deep as SET. with this amp in place R&R comes to life, FZ is very dynamic no compression now, however less magic on acoustic music still sounds very nice but.. Doc Watson guitar and voice on SET amp, Wow. The separation on the ARC amp is a compromise, there is only one input tube a 12AX7, there was not room for nor power for 2nd tube. WZ Johnson stated he would have liked 2nd input tube, would have made this closer to I believe a D-79?

 

[Lavane]

I hadn't seen that ST-70 mod before.

 

[kcline]

I ran the ARC St-70C3 for a few days, does run a little warm, not the best amp for hot weather. Next amp up is one of my Fisher SA-100s, again using the Line Voltage Corrector as this amp runs very hot so I ran it at 114 volts drawing .09 amps with this setup amp ran much cooler then 120 ac operation. This amp has had a hard life, first it was cut up for a power supply ?? then it was given back in pieces to first owner who welded back chassis and rebuilt using new parts except for the iron which was never used in the PS. Anyway has a mixed bag of 7189 tubes but they are a matching quad. Unit has very nice sound after warm up nice wide soundstage good Depth acoustic music is nice all the power you need there and enough power for R&R, to me not quite as good as ARC amp as all around amp, low end better with ARC and most everything else about equal. This is not a totally fair comparison, the SA-100 was rebuilt with what ever was there that would work, while with the ARC amp, the best parts and tubes are used. Sorry for the picture

 

[kcline]

I did learn one thing, running the SA-100 with the Line Voltage Corrector at 114 volts it took 4 hrs for amp to get really hot , need to get my other SA 100 restored it may be next in line. Due to the heat I have placed the 45 SET amp. back in as it does not get hot at all, played this setup early today for 3 hrs or so, very nice relaxing sound and it did not heat the room up

 

[Nyjblbob]

The best way to use a 45 amp is Biamped just on the mids and tweets. any other amp for the woofers.

 

[kcline]

Played 45 SET amp this past weekend, too hot for other systems, had go to "radio world" Saturday, my partner in all things radio. I had two to pickup and I took him some # 80 tubes. Then I looked thru his collection of 6J5 or 6C5 tubes found two metal 6C5 that I gave him from a case of the same, that I took home. 6J5 and 6C5 are the same specs. more or less, but according to RCA are different, inside a 6C5 are the metal parts of a 6J7 triode connected with grid G-3 removed. 6J5 is approximate a 6SJ7 triode connected but not made from those parts. Ok for my almost final tests on this amp I placed the NU ST-45s back in as the amp is fine tuned for those, I pulled out the 6J5-G tubes and replaced with metal 6C5 RCA, these are also stamped on base 6C5, I have seen 6J5 stamped on base of 6C5s and I have seen it the other way too, I always look. After warm up I played for hours a lot of LPs folk rock Moog more of the same I have been playing Wow, amp with these tubes, the 45 NU St and NOS 6C5 are the best sounding. I will leave this as is for now

 

[Poultrygeist]

Depending on the music flea watt SET amps can struggle with bass. That's one reason I bi-amp with a more powerful ss amp augmenting the low frequencies.

 

[hogwylde09]

Thought I would search the forum for the Type 45 SET amplifier users. The Yamamoto a-08s has no issues producing bass paired with Klipsch CF4’S.
It uses the small “door knob” looking 717a input drivers. Managed to get it with a pair of Emissions Labs EML45, small extra fee. The solid plate version.
Correct about the styles of music sound best in the flea watt powered amps. With the right slower tempo styles, it is as if the speakers virtually disappear from the room. Near field listening, 8-10 feet away. The speakers about the same distance apart, towed in.
I’m only steaming Hi Res files from Amazon HD Music or Apple iTunes subscription. Asus Essence STX II sound card (the software control panel set in HiFi mode, completely flat eq) sounds stellar. And most likely at maybe 1watt. Provided the source material mix is HQ. Any flaws are revealed immediately.
Since it’s a stand alone amplifier this is the way I’m using it for control of volume, and only one input device for now.
I do have an passive 4 input stepped attenuator preamp on the way, albeit China model. As to add more devices.
This is a huge dramatic change in the way I hear the finest detail in music. Something I’m really new to.
Don’t get me wrong, I have plenty of other tube systems for turning up the mighty rock, MC30’s, 75’s
Fisher 400 with Klipschorns. Great tube preamps. All with tone and loudness controls.
I never, would have imagined in my lifetime enjoying that “ first watt that counts”.

 

[Dave451]

I had a chance to try out a Mark Eaton 45 SE amp a little while back and was very impressed indeed by the quality of that 'first watt.' The amp had range and detail I wouldn't have imagined into my Klipsch KG4's and Cornwalls. 6SN7 front end.

 

[Poultrygeist]

If you like the 45 you'll also like a 2a3.