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At least that's my nick name for it. I have started going through my collection of SP magazines again like I do ever few years. Last night I was looking at issue Vol. 2, #1 and saw J.C. Morrison's article on his design for the dinosaur amp. I noticed that he advocates running the chinese 845 tubes "low and hot". Low voltage and high current. For the dinosaur he suggests operating points of 500 vdc plate volts, 88 mA plate current and -50 vdc grid volts. I am thinking I just might give that a try on the 26/26/845 I have on the bread board as the power tranny I am using can get there and I think I have caps rated high enough. Wondering if anyone has run a 845 at these operating points before? JC claims this is a good way to get great sound from the 845. It sure puts you in a linear region of the plate curves from what I can see.
Setting it up on SE amp cad it appears to be well below the max dissipation curve for the 845.
I would be interested in hearing of anyone's experiences along these lines.
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Somewhere between 6-9 watts? I bet that amp sounds awesome.
It does play with an authority that I attribute partly to the higher output wattage and partly to the 845. I am really curious what a full blown 845 would sound like, but 1200+ volts B+ is not something I want to mess with.
I can live with this lower voltage version.
for a 845 mono block build, I just need the output transformers and the ones I'm looking at are expensive. I still may visit the project down the road.
The design would have gave me around 25 watts but that dc voltage would be very high. So like you, I may look into doing a low power one.
I hear once the 845 are driven properly, they are sound heavenly!
Naz
Hi Naz, I just finished my Bob Latino VTA-120 kit so I finally got my little experience with building a tube amp from a kit. Now I'm ready to take on that 845 project you and I were discussion a few years back with that schematic for the 845 amps with 1000vdc. :)
I learned a lot from this build. One was to pre-clean and pre-tin all leads. I found out the hard way that the wire that was supplied was pre-tinned but it melted at a different temperature than the solder I was using so there was two cold solder joints on the heater lines going into the pcb.
I used a Chop stick to probe/poke around since the solder joints looked shinny and good. The chop stick works very well as I found the bad joints really fast without having to stick my hand in the unit since there is 500vdc. After using a magnifying glass I saw what the joint really looked like, the solder flowed nicely all around the wire but never melted together. So the VTA-120 is up and running and sound really nice.
I still have all my parts for the 845 amp build and will be looking into some output transformers for this build. These output transformers are expensive!
That's great, because I'd hate to encourage you into a build you you weren't ready for. For mine, the risk difference between 500V and 1,000 is not as great as one may think as either can kill you. Others will definitely differ on this point and I would not argue but the benefits are worth it IMO.
I know that the OP trannies are expensive but they are also critical and an amp like this deserves decent trannies. What I can attest to is that over the years there's been many an occasion to compare my 845s directly with any number of well respected and some extremely expensive amps of all kinds and nothing (other than one or two of my other SETs) has been remotely close to the clarity, authority, balance, dimensionality and sheer musicality of the 845s and that doesn't just come from me. As such, even though I know there's always better I have not felt the need to even tinker with them for many years.
Anyway, I'm glad that you are have made great progress and if and when you are ready I'm happy to help as much as I can.
Cheers,
Naz
And chassis then I can start the build. I can wait for the output transformers until a later date.
Thank You for the offer, I will surely take you up on it and I may lean on you pretty hard since I'm still learning this high voltage amp thing/s.
I do have the proper work bench now (all wood) and associated gear for the test bench.
I'm really enjoying the build and sound of this VTA-120 amp and can only imagine what a 845 SET amp will sound like. I sill need to finish my two way horn speakers project. These speakers should be a great match for this amp or SET amp.
I will PM you when I get ready to start. Thanks again!
Low voltage 845 driving low voltage 845?
Quite a project, more involved than I am likely to get with mine. Thanks for the link.
Well I went ahead and dialed it in, and I can't say I really heard that much difference from the version using plt 430, grid 51 and current 62 mA. There was a bit more gain of course, and I think the bass might have been a tad cleaner, but nothing really earth shaking. Soooooo, that leaves me with the question if I can change the operating points by that much and not really hear much difference, how critical are they?
Yo Vinnie Here's my 3 stage Low voltage stereo 845 amp. It's 6sn7 Directly coupled to a 2A3 and IT coupled to the 845. It run at 600VDC on the 845's at about 72ma. I didn't want to use a higher B+ than 600VDC.
It sounds very nice, like a Big 45. I have to use a preamp to get it to play at loud volumes. But fun!
I prefer my 26-26 DC 45 amp !!! JMHO !
Willie
Hey Willie
Nice looking amp. I wanted to stay with all dht as I have been captivated by their sound. I have been A/B ing my 26/26/45 against the 26/26/845 with a mono source by hooking one channel of each to my preamp and switching back and forth between them with the volume controls. To me they are quite close, but I like the overall sound of the 845 just a little bit better I think. I could be happy with either though.
....maybe if your 26/26/45 amp were a better build, you might like it more !
I'm just saying!
Have fun
Willie
I'm curious Willie, what makes you think it isn't?
Edits: 09/19/16
its all about the build. Ver.#1 got me hooked.
Ver.#2 is at this stage is the "Bomb" dynamics galore ,pace, and purity of tone ... Yes, Yes, Yes...
It's all about the build I'd like to think this is a better build than the Ver. #1 ...... It shows up in the sound
Have fun
Willie
I think this is a pretty good build don't you?
...Yeah looks nice ......But it doesn.t look like it's built for "Speed " !
Willie
You are going to have to do better than that Willie.... details if you don't mind.
You might want to contact Jeff, he had a 2 stage Low power 845 design.
Willie
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