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This is a real near-mess.
Virtually EVERY tube has its fans and detractors. Very little actual concensus exists.
Here's the LAST one of thiese I've found
Rectifier tubes. Many trains of thought on this UNTIL you toss in Solid State Recitifers. Even the guys to make 'em don't necessarily agree....
Just for example? Several choices exist for the venerable 5AR4. One of the big guys in this space makes a few replacements for this tube. A Thermister is optional and at least ONE of the replacementss is NOT recommended for HiFi. Though some DO use it in that application.
I kind of LIKE the idea of a SS rectifier, but to do it right, you apparently need a TIME DELAY relay for the high voltage, to give the heaters a decent head start.
Too much is never enough
Follow Ups:
Are you keeping your Maggies or still considering the Klipsch Forte?
You know the latter was recently upgraded to the IV? With the high efficiency that could simplify your amp needs, but I don't blame you for wanting to audition them first.
Regarding your rectifier question, this may be circuit specific (I don't know enough to say) but I'll offer it for thought. When my friend Jud had Joule Electra, in the early days he offered two similar line stages. The LA-100 was all tube while the LA-75 had SS rectification. Very few preferred the LA-75, saying it only worked well playing R&R. He soon discontinued that due to very low demand.
Anyway, good luck.
"The only cats worth anything are the cats who take chances. Sometimes I play things I never heard myself." Thelonious Monk
Yes.....100%.....Will I like the Forte IV enough to part with my panels?
And yes, again....My current amps, a PAIR of A23 Parasound is quite a bit of amp for such speakers.
I'm considering the VTA ST120, based on the Dynaco model with some meaningful improvements.
Better iron and more capacitance, as well as ability to run 6550 / KT88 and a few other output tubes.
If you were still in town, I'd ask you to join me for a trip to the nearest Klipsch Heritage dealer, maybe 80 miles to the north.....
Too much is never enough
Not all SS diodes are the same. Standard diode makes a lot of noise unlike a tube. Hexfred or CIS Schottky make little noise just like a tube. Yes, you can hear the difference.
I trust your opinion and enjoy reading your comments. So thanks for that.
Have you done, or know of any testing to see exactly what the REAL world effects are with various diodes in the PS. Are we talking about audible noise or some ringing in the 50kHz range?
Compared conventional diode to Hexfred and CIS Schottky. The Hexfred and CIS Schottky had a slightly, but noticeable quieter sound. All diodes feed extra large capacitors. If the caps were factory stock capacitance, the difference would have been larger.
I don't expect you to do it, but it would be interesting to see some scope tracings on an "average" stereo with and without low noise diodes. But who feels like taking that much time out of our week when we're talking about a difference of a few cents in diodes.
Conventual diode- 50 cents. Hexfred or CIS Schottky- $6.
I MANUFACTURED the HEXFRED while working for International Rectifier, prior to the sale to Infineon.It was a relitively quick process (number of steps).
It is or SHOULD be a commodity cheap product. 12x a conventional diode is ridiculous. The main
source of increase in cost is the EPITAXIAL Silicon used as start material....But each wafer held LOTS
of potential parts....And since the process was so simple, we got Very Good yield, indeed.
Don't let anyone tell you they are 'Expensive' to make or whatever. In-Fab yileds are high as are
probe yields. The MOST expensive part is the start wafer. We would start 'em 100 x 6" wafers at
a time. A single lot would yield THOUSANDS of parts. And require a fraction of the time and steps
used to make a MOSFET......or in our case.....a HEXFET device.
Too much is never enough
Edits: 07/28/21
I worked for a compamy that manufactued discrete devices.
I helped make more HEXFREDs than you could possily imagine.......
a 6" wafer held maybe 500 to 1000 usable die and each 'lot' was 100 wafers.
Being a simiple process, the yield was good......And resulted in what amounts to a commodity cheap product.
Too much is never enough
As long as the amp is properly designed for either - what's the problem?
I'm beginning the think you should stick with your present system.
I read a LOT. And you should see some of the stuff about rectifiers both tube and SS.
Some swear by NOS Mullard or some such while others modify the 'Copper Cap' Weber SS device.
I'd like to LOCK a bunch of these guys in a room with ONE key out.
You shouldn't worry about my 'process'. It usually works in the end. The trick is to make Marginal OCD work FOR you. Research is good, even if you toss much of it in the end.
What got me started were various posts about how much current DOES or DOESN'T such an amp need. Most of it was about increased current needs of output tubes like the KT120, where I'm NOT even thinking of going.
Next Step? Drop 'up' north to OC or LA and listen to the KLIPSCH Forte IV speakers. And perhaps others in the HERITAGE line. If I hate 'em? No Move. but I won't run such high sensitivity speakers on 500 (8ohm) SS watts.
Too much is never enough
Below is a link to a Hammond chassis which is larger (17" x 10" x 4") than a ST-70 chassis, and I think it's better looking, unless you're REALLY into Dynaco nostalgia. It would give you more room to work, you'd be able install a higher value choke, and perhaps even two 5AR4 rectifiers. It's on sale for $86.42 at the moment.
Since it's made of aluminum, you'd be able to put in the IEC AC inlet of your choice, and still use the VTA, or some other input circuit. Dynakit parts sells a transformer kit, and so do some other places. Another nice thing about a larger chassis is that you could actully fit a binding post for the 16 ohm tap on the back, in addition to the 4 and 8 ohm taps. Notice on the current version of the ST-70, the 16 ohm tap is capped off internally because there isn't room for the two extra (larger) binding posts.
Rather than buying a kit, and immediately start modifying the chassis, giving yourself a "proper" sized chassis from the onset will make your experience easier, long term. I can't vouch for the quality of the Hammond, it's more about giving you other ideas.
A terrific idea, at that.Need to do some MORE obsessing and reading.
Wonder IF it would be possible to buy a PAIR of the M125 MONOBLOCKS from VTA and put 'em BOTH in a single chassis?
It'd take 2 men and a boy to move it, but WOW........
first? The wooden side panels are Beautiful. Finish with Teak oil and do a quarter round treatment on ALL exposed sides? Nice.
Downside? ALL THOSE HOLES in the rite spot AND of the perfect size. It would be neat to mimic the orignal layout with just a LITTLE more space in some places. Room for a bias meter, too, with switching. And if you went with the SS rectification, plenty of room for the time delay relay board.
Let me look up some other things to get an idea how much $$ more this'd be than the VTA amp.....
Too much is never enough
Edits: 07/11/21
Excellent idea! Wiring the power supply and output stages is straightforward, and driver boards can be purchased off the shelf if you don't want point-to-point in that area. And being as you both raised the issue of rectifiers, I would strongly consider using two 5AR4s in any ST-70 clone and adding PRV diode protection.
Yes, people online argue all day long about insignificant details, and most have absolutely no evidence to back up the supposed benefits of what they propose. You won't go wrong if you stick to the basic requirements and keep it simple. :)
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Buy Chinese. Bury freedom.
I think that a step back might be in order. You're leading an OC engineer away from a simple kit build to redesigning a power supply. And you know that's just for starters. It's going to take this guy years of obsessing to get this thing working.
My neighbor is an EE and an OC type. I know what's coming and it's not going to be sweet music. My neighbor can tell you how quantum switching works but he can't fix a toaster or solder a wire.
If this guy is unhappy with this kit then he should move on. Perhaps buy himself a nice built tube amp and then hobby build this thing on the side.
At least I have the Advantage of having learned to Solder from a Mil-Spec rated person.....
And after having owned a Unger Imperial Iron (relic) I finaly broke down and bought a real Hakko soldering station....
Too much is never enough
"Wiring the power supply and output stages is straightforward"
I meant to add that to my reply, that the original Dynaco ST-70 assembly manual has step by step instructions, so a beginner could have that resource to follow in addition to the schematic, if they need it.
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