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Hi all,Here is my latest build.
It is a 1625 SE triode strapped amp.
Made from a sustainable tropical hardwood with a Class A fire rating.
The sound is clean, clear, transparent with good texture and timbre. Bass is tight and low, not flabby.
It is wired using magnet wire and terminal strips rated for 600V+
Mains wiring is done using stranded 600V+ wire.
The thin signal wire from RCA jacks is teflon insulated Cat VI data wire
Power supply is 230VAC voltage doubler for a 515 B+
2 3DG4's are the rectifiers
Pramp tubes are 6ER5's
Power tubes are 1625's (837 and 802's can be used with modification of cathode resistors and heater arrangement for the 802).Anode caps are held on by copper tubes going through a collar and set screw. A high voltage rubber insulated wire is fed through the tube.
The clips were taken out of the caps and the stripped part of the wire is firmly sandwiched between the cap and anode. The cap, tube and tubing does no moved, even when wiggled, once the set screw is tightened.
Plus no clips to pull the tube anode off the tube.Any comments and questions are welcome
Normality frightens me- its what they use to lure you into the cookie cutter.
Roger
Edits: 05/02/17Follow Ups:
You don't usually see transmitting micas in an audio amplifier. Nice layout!
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Buy Chinese. Bury freedom.
Thank you Triode Kingdom.Is there a reason why you don't see many transmitting silver mica caps in amps?
Normality frightens me- its what they use to lure you into the cookie cutter.
Roger
Edits: 05/02/17 05/02/17
"Is there a reason why you don't see many transmitting silver mica caps in amps?"
They're just not part of the typical audio retail offering. They're larger than necessary due to the voltage ratings and more difficult to use than components with axial leads. Also, if memory serves, that style is not silver mica. They're just HV mica transmitter caps.
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Buy Chinese. Bury freedom.
Awesome information!
Thank you.
I'm guessing that regular mica would sound different than silver mica...which may be why it sounds a tad harsh to my ears. The owner-My Mother- likes the way it sounds...but she is used to solid state. Polypropylene may be the way to go this time. Silver mica always sounded fine to me.
Normality frightens me- its what they use to lure you into the cookie cutter.
Roger
I'd be extremely surprised if anyone could hear a difference between standard mica and silver. Silver mica was used where a more stable temperature coefficient was needed, such as RF oscillators and high frequency tuned networks. There's no difference otherwise in performance.
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Buy Chinese. Bury freedom.
What is your opinion on the sound of mica/ silver mica used as a coupling cap, as used in this circuit?
Normality frightens me- its what they use to lure you into the cookie cutter.
Roger
nt
Using a 6.8uf cathode bypass cap on the 6er5 gives a -3db point of 40Hz for that stage which, BTW, matches the -3db point of your speaker.Also a 6gk5 is much more linear than a 6er5.
I like the steampunk look.
What gauge magnet wire are you using?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 05/02/17 05/02/17
Thanks Tre,
I will look into the 6gk5. I believe the gain is less, but still substantial. I'll also look at pin-out and optimum operating points.
I'll also look into a larger film bypass cap.
I'm using mainly 18ga. magnet wire of three colors. I used 16ga. for some of the heaters, but 18ga. seems to be the best for workability and current ratings.
Normality frightens me- its what they use to lure you into the cookie cutter.
Roger
Roger
Very nice! When I first looked at the second 3DG4 rectifier tube,I wondered what it was doing there and then I realized it was part of the doubler circuit.It is very confusing seeing tube rectified doubler stacks.
Have you considered a couple film caps in the power supply down stream.They make them smaller in size now and you have lots of room in that chassis.I like the layout of this amp. What are the two woodgrain looking brown things that look like STK ICs with no pins? Are those EMI filters?
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 05/02/17
Thank you for the compliments Michael,
I know it is not often that tubes are used in a doubler configuration.
I'll look into the film caps. Motor run caps are also good caps, polypropylene, but are large.
The brown hexagonal things are vintage silver mica caps- 33nf 600V
Normality frightens me- its what they use to lure you into the cookie cutter.
Roger
Kudos. A very nice build.I've never seen anybody use a relay tube. I take it allows the heaters to warm up first before the HV hits? Cool. I wonder if that would work well for DHT direct coupled amps?
Man you're right, those anode caps aren't going anywhere! :)
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Big speakers and little amps blew my mind!
Edits: 05/02/17
Yes, they do work well and a perfect complement to a vintage design.
Can be a bit hard to find though.
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Big speakers and little amps blew my mind!
Thanks Mr Steady,
They work well, easy to wire and look nice. I was lucky to run into a couple. I've also seen some on sale at tube suppliers...the main manufacturer is Amperite.
They come in different heater voltages...the one I'm using here is 115V heater.
Normality frightens me- its what they use to lure you into the cookie cutter.
Roger
One potential issue with delay relays has to do with the relatively small contacts. For longest life, it's a good idea to use a larger relay to turn on the HV transformer. I'm getting ready to add delays to my own SETs, and have decided to go even a step further. The delay relay will power a main relay, and that one will be wired so it latches electrically. In addition, one set of contacts will be wired to disconnect the delay relay. So, once the amplifier is fully operational, the delay relay will power down and cool off. Not only will its contacts only need to pass a few mA to activate the HV, its heater will only be used for a minute or so each time the amplifier is turned on.
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Buy Chinese. Bury freedom.
You said
"One potential issue with delay relays has to do with the relatively small contacts"
Correct that also includes SS time delay relays.
You said
"The delay relay will power a main relay, and that one will be wired so it latches electrically. In addition, one set of contacts will be wired to disconnect the delay relay. So, once the amplifier is fully operational, the delay relay will power down and cool off. Not only will its contacts only need to pass a few mA to activate the HV, its heater will only be used for a minute or so each time the amplifier is turned on"
The disconnection of the delay relay is simply overkill I've run a similar scenario using 24V/30A relay activated from SS delay mains relay / timer for 10 yrs without fault. You can safely derate the DC current rating by 50% into a inductive load ie transformer and still be well under the DC rating. Relay coil DCR for 12-24V are under 1k ohm so the current requirement are small. But install a diode - reverse biased across relay coil to absorb back EMF on turn on / off. Seriously this configuration has been used in cross bar / step by step electro-mechanical telco exchanges for generations....bullet proof.
Johno
Disconnecting the relay heater after it closes has the additional advantage of resetting the timer. This means that the timing cycle will occur on a brief power interruption as well as cold turn-on.
"...the timing cycle will occur on a brief power interruption as well as cold turn-on."
Exactly right. The main relay will drop out instantly in the event of a power failure, then the delay relay cycles again. This is necessary in order to be sure the DHT filaments are always at full temperature when HV is applied.
About Johno's comments, none of the glass delay relays in my stash have contacts rated anywhere near 30A. Most are probably 3A, and that's probably a non-inductive rating, perhaps DC. I've also noticed costs rising for these parts, and I wonder if replacements will be easy to find in 10 or 20 years. Call it overkill if you want, but all things considered, I don't regret taking the necessary steps to see that these last as long as possible.
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Buy Chinese. Bury freedom.
I forgot to mention the VR tubes regulating the 6ER5's
Along with the tube relay that can be seen from behind.
Normality frightens me- its what they use to lure you into the cookie cutter.
Roger
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