Replica Dynatron amps

[HoverJohn]

Hey folks I’ve been really impressed with the performance of the restored amp in the Dynatron (mono) and I was contemplating building a pair of amps for stereo use using as near as possible original spec. However I was wondering if embarking on such a project would you still go for valve rectification on the HV or diodes? Also would it be better balanced using a single power supply for both amps (ie all in one box) or am I better keeping both channels isolated in separate chassis and balance them up using matched components etc.
similarly if building a stereo version of the pre amp should I keep it isolated so one channel goes through the same 2 stage vale twice or put both inputs into the same valve then again into the next etc??
Also I have access to an engraving machine that I could carve up some good quality heavy tracked circuit boards would you do this or keep it spaghetti in side?

[Analogue man]

Personally speaking I would keep the left and right amplifiers separate including their power transformers if you can afford to do that. Also, with the preamplifier I would be inclined to try to keep a valve to a particular channel rather than one half of a double triode on the left and one half on the right but again money has a baring on what you can do. My own valve amps all use solid state diodes for HT rectification, but it is a matter of personal choice. As I say this is what I would do but it is your amplifier and your money. I personally would not engrave circuit boards as this could weaken the board, a good chemical etch is IMHO far better although due to the high voltages in a valve amplifier I would consider using hook up wire instead.

[Radio Wrangler]

The real money and the real difficulty will go into the output transformers. Mains transformers are not so critical, but in a listening room you'll want them to not hum and clatter.

A stereo amp or two monoblocks? The stereo approach with an amalgamated power supply was OK for Harold Leak, but the result can be ungainly, so monoblocks may be more practical. Will it/they sound different? Not if you engineer things well enough, yes if you take horrible short cuts.

Valve/semiconductor rectifiers? If you are going to thrash the thing to the point where the HT is pulled down and it affects the sound, you may want valve rectifiers. You are probably a guitarist. However, what sounds dramatic on a single instrument, sounds abysmal when one loud instrument pulls everything down with it. So you probably don't want to go into the areas where valve rectification is preferred. So there's nowt wrong with semiconductor rectifiers. Use fast ones for low radio interference. Also remember that HT will come up before valves warm and current gets taken. Make sure capacitor voltage ratings are sufficient and you're OK.

Layout? Stick close to the original. Stray C will affect high frequency phase shift, affecting stability, flatness, ringing. Grounding and power paths will affect hum as well.

Preamp? The old valve designs were very limited to keep component count down and to avoid complexity. Modern transistor designs have no implicit disadvantages and can be a lot better than classic valve designs. NE5534 opamps are excellent though 40 years old design, difficult to improve on, and most of your music will have already been through several. Anathema? Heresy? but true. This survives scientific measurement and extensive, skilled, listening tests.

David

[HoverJohn]

This is all great stuff I will consider layout and keeping the power away from the more sensitive parts hoping that the Circuit board will mainly house all the smaller bits that were usually crammed in together anyway and keep the transformer etc outside the chassis- is this why the rectifier tube is the opposite end to the first stage amp tube 12ax7 etc.
I really fancy making the boards as elegant as ossicle but accept that HV bare conducts might not be a great idea.
While on the interference topic - traditionally they are all built with solid wires but multi core or braided is supposed to have less issues is that with considering? I was thinking of poly carbonate chassis but that would have zero shielding capabilities!!
One big issue will be finding a pair of good output transformers and suitable power transformers.
Also when the radio unit Is unplugged on my old Dynatron the HV really goes up so was wondering if I need to manage that some how if the design is otherwise the same.

Oh and it’s for audio use - but I do like it cranked.

[Analogue man]

A metal chassis is a must but a polycarbonate over skin would be fine provided it can take the heat from the output valves which will get very hot.