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Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 12:09 pm
by Alfi
SteveTheShadow wrote: ↑Sun Apr 05, 2020 11:25 am
Like one or two others on here, I too have been at it with the DIY. I built myself a nice, 6W, single-ended KT77 valve amp out of bits I had lying around. No new bits were involved in this project. The blue transformers were painted with an old can of smooth Hammerite, I found in the cellar. The wood chassis housed the OTL. I just lifted out the OTL chassis after disconnecting it and dropped this one in its place.
It uses separate power supplies: one on the output stage, fed from the blue mains transformer, silver choke and large 5U4G rectifier valve at the rear right, and another, on the input stage, fed from the other blue mains transformer, and small EZ81 rectifier at front right. The choke for the input stage supply is under the hood, just behind the EZ81.
The pair of Genalex reissue KT77 pentodes are triode wired and fed by the pair of parallel strapped, 1960s, Hitachi 6SL7 twin triodes at the front. It partners the single driver Fane speakers nicely and gives a big, warm, detailed and musical presentation.
That turned out beautifully Steve and the Hammerite paint colour and execution of application to the tranny's is superb, really looks professional!
Jewel pilot lights look cool too, reminds me of my Fender Princeton guitar amp - knockout!
Alfi.
Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 1:32 pm
by Daniel Quinn
I would like a real world example of costly and dangerous, please.
Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 1:37 pm
by valvesRus
Daniel Quinn wrote: ↑Mon Apr 06, 2020 1:32 pm
I would like a real world example of costly and dangerous, please.
Dangerous = stick one's finger in the wrong place =
DEATH.
Is that dangerous enough for you ?
Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 1:42 pm
by Vinyl-ant
Alfi wrote: ↑Mon Apr 06, 2020 12:02 pm
Doc stated in an interview with Audio arts magazine in 1992 that he could hear ripple and is why he kept cap value to a minimum, (which surprises me) as I always thought bigger cap value = more instantaneous reserves of power = better transient response?
Alfi.
Bigger caps also equal longer charge time. A bass frequency will need more current to reproduce, a big cap can supply the juice, but takes longer to recharge after discharging to supply that peak. It's a balance between being able to supply enough current for one peak and charging fast enough to supply the next peak.
Big caps mostly equal big physical size so that's a consideration. Massive caps may be able to supply several peaks but relatively speaking take ages to charge up again.
There is a school of thought for huge value low esr caps, and one for small value very fast charging caps.
You would be surprised just how much psu headroom a phono stage needs. It's not a great deal less than any other amplifier
Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 1:52 pm
by valvesRus
One thing that some builders do is have resistors across the PSU capacitors to drain the charge away when the amp is switched off.
I can remember getting a belt off one of my Quad 11 valve amps weeks after it had last been used.
Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 4:34 pm
by SteveTheShadow
Alfi wrote: ↑Mon Apr 06, 2020 12:09 pm
...Jewel pilot lights look cool too, reminds me of my Fender Princeton guitar amp - knockout!
Alfi.
Yes, I realised quite a few years ago that the guitar people, including both players and custom amp builders, know more about tone than I could learn in a month of Sundays. That’s why my most successful by far valve amps, including this one, and a pair of 6B4G monoblocks I built and dismantled years ago (fool) have been built with guitar amp components such as Sprague Atom electrolytic capacitors, JJ dual element 500V can caps, Mallory 150M series polyester, or Sprague “orange drop” signal coupling caps, carbon film and carbon composition resistors and Ohmite wirewounds.
I don’t use audiophile components of any description any more because:
a) I can’t afford such stuff these days.
b) IME they have too often often fecked up the music.
I like a good warm, saturated tone colour from my valve amps, and guitar amp parts just seem to do it beautifully. They don’t tend to cost the earth either.
Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 5:43 pm
by Daniel Quinn
valvesRus wrote: ↑Mon Apr 06, 2020 1:37 pm
Daniel Quinn wrote: ↑Mon Apr 06, 2020 1:32 pm
I would like a real world example of costly and dangerous, please.
Dangerous = stick one's finger in the wrong place =
DEATH.
Is that dangerous enough for you ?
Please for the sake of everyone , dont reply with such benalities
Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 5:50 pm
by valvesRus
Daniel Quinn wrote: ↑Mon Apr 06, 2020 5:43 pm
valvesRus wrote: ↑Mon Apr 06, 2020 1:37 pm
Daniel Quinn wrote: ↑Mon Apr 06, 2020 1:32 pm
I would like a real world example of costly and dangerous, please.
Dangerous = stick one's finger in the wrong place =
DEATH.
Is that dangerous enough for you ?
Please for the sake of everyone , don't reply with such banalities
At best you could get a nasty electric shock, at worst it could kill you. No point in fannying around to make it seem less serious.
The normal advice is to wear rubber gloves and/or keep one hand behind your back.
Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 6:19 pm
by Lurcher300b
Bigger caps also equal longer charge time.
They shoudnt do if the current capacity of the transformer feeding them is chosen accordingly. If designed correctly, they should still charge back up over the next 100th of a second charging cycle.
which surprises me) as I always thought bigger cap value = more instantaneous reserves of power = better transient response
More reserves of power, but what matters as much as the size of the capacitor is its ESR and even more important is its inductance they will both restrict the caps ability to respond to changing loads.
that he could hear ripple and is why he kept cap value to a minimum
I don't understand that as smaller cap value equates to more ripple. If he was still here he might well respond with a entirely different definition of ripple to the rest of the EE world. Of course cost may play a factor as well.
Re: Lockdown Valve Amp
Posted: Mon Apr 06, 2020 6:36 pm
by Alfi
Daniel Quinn wrote: ↑Mon Apr 06, 2020 1:32 pm
I would like a real world example of costly and dangerous, please.
One can blow things up destroying pcb's and other components. Plus you could kill yourself (as valveRrus already said) if you don't really know what you are doing!!
Alfi.