isnt the purpose of large (wattage) resistors in the power supply side usually to keep the rectifier tube happy? something about the charging peaks on the 60hz waveform can exceed the current capability of the tube and cause it to prematurely fail because you are trying to charge in a short time? at least thats how it was explained to me.
if you go with a large solidstate bridge dont you essentially do away with this limitation up until you start popping fuses from initial surge when you first turn the amp on?
ke4mcl, As I did reply to you earlier I had forgot to say that I grew up in North Miami, FL. I had two HAM Radio operators at both ends of the block that I lived on. As a kid I was fascinated by short wave. But today its glass audio with transmitting tubes:thmbsp:
I've seen rectifiers arc over. It's pretty but expensive. My 4 year old son was all excited and asked me to do it again!
Yeah I have seen a tube literally start on fire as the glass had cracked. Another friend had one his Tube Acoustat Monitor X amplifiers start on fire while he was away even though it was in standby mode (heaters just on) I owned a pair of these as well. Moral here is "never leave a tube amp on alone"
There's no resistor in the B+ supply of the Eico to eliminate.
That was exactly my point, There's only the power transformers and tube rectifiers DCR for a time constant. That generates dynamics!
I once lived in a side by side duplex that had the two living rooms separated by two garages that were between the both of them. I was listening to some jazz with acoustic bass and my neighbor lady called! She said the pictures were moving on her walls! That was just from my 10 watt amps pictured in my avatar. I use no EQ and no subs! That's with a pair of Klipsch Forte's which today are like a thoroughbred race horse.
I'd opt for a low resistance choke to replace the 100 ohm resistor in the Pilot. If you found something in the 25 ohm range then the B+ voltage swing from quiescent current to max current would be about 0.5v. As a bonus you get less ripple and no chance of frying a non-NOS high zoot rectifier.
Yes, its a nice value 25 ohm DCR to start, but 25 ohms is nearly half the DCR of most power transformers I prefer even less like 5 ohms!
I find most people go with to large of chokes (Henry value and DCR0 IMO , I once use to my self. A 500mh choke is more than up to the task of removing what a 100 ohm resistor does
Ripple tolerance or noise is a personal tolerance. Often times a very quite tube amp is one that sounds like its strangled IMO and and one with some or a bit of noise is the one that makes my toe tap. And I'm not the only one to experience this.
So subjectively one can have the numbers make you happy. But for me its the subjective experience that gets my toes taping. I like understanding reasons and I think I have found a few IMO.
I must be doing the math wrong because on the Pilot schematic it looks like the tube is dissipating over 15w. Is that right?
Yeah, that's what it says but of course its wrong, I seem to remember measuring 10 volts at the cathode on my buddies Pilot. I can't remember if we used 150 ohms but probably. In that case it would be near 9.9 watts of dissipation the RCA RC-30 tube manual says 125 ohm self bias resistor with 72ma of current (both tubes)for an AB1 class amp that would put the cathode at 9.37 volts.
I have two almost-identical GE amplifiers, one that takes the B+ straight from the first cap, and another that I modified to add an additional filter stage with a 50R resistor and 100uF cap. I prefer the latter, it sounds much cleaner. The first one is a bit "faster" / "ballsier", since it sags ~10% less, but eliminating some of that power supply noise, and increasing decoupling, really cleaned things up. So, my preference is somewhat opposite. However, I think if you filter the crap out of everything but B+, and have bias/balance controls, then a single-stage filter can work very well indeed!
Hi jon_s, I guess that's a personal call and what you want for performance criteria there's nothing wrong with that! I couldn't live with a 50R in the path of my amps.
Filtering the crap out of everything in the classical circuits with large volume is not an answer either as many all to well know.
But there is a way it can be done and be as fast and transparent as small caps yet far more authoritative.
A lot has to do with the total system, its the the weakest link issue. Meaning if the rest of the system isn't up to par the less likely one is to hear changes IMO, we all have weak links I think I just have fewer than most. We are always working on them thats why we are all here.
BTW, install an inrush current limiter, or your 5AR4 will arc over the first time it gets power cycled while hot. The slow start doesn't work if it is already warm, and a quick power outage could be a $100 instant loss. My non-vintage 5AR4s arc with 60uF caps when power-cycled.
Yeah , when I first got some new stock 5AR4's (does not meet NOS spec's) I experienced the same issue. No doubt the inrush limiter works, but so does waiting a few minutes as well with an NOS providing there is enough slow turn on delay.
Actualy ,the limiting factor for current is the rectifer tube and the power transformer ,use a toroid and solid state rectification to gain more current and then add all the caps you want .The amp i'm building has a one amp toroid per channel for the B+ and and 1,400 mfd for the first cap , five times the current the output can draw .
Looking at your Bio I see you live in the St.Louis area, my daughter lives in that area as well. I work in the electronics manufacturing industry and work with former radar technicians like yourself as well.
Gordon does have point! IMO, When a given circuit is used and big changes are made one often doesn't get what they expected! I can a test for that! But then again I have seen monstrous results as well, but that depends on design applications that achieve the desired results.
In my early days I fooled around with big caps and such! But I found out fast just how ugly they can sound. I found it was better sounding using groups of small volume caps and later I discovered what diode isolation can do for an amp with monstrous volumes of capacitance and then use premium Poly's to run the gain stages as though the high volume electrolytic's were not even there!
Its really an art that sometimes takes yrs to develop, we all started some where!
As to sand rectifiers I use them but only if I feel I have to! I just prefer the harmonics of a tube rectifiers.
They can and I do use them with high volume capacitance. Its how you put them to work whether the live or they die and how long you want them to live! 20-30yrs or 5-10yrs, I'm not working for them I want them to work for me!
Interesting thread. To me, power supplies are very important, and one of the best places to get "bang for your bucks" from simple mods. The only place I ever use a resistor is for the front end B+ where current demands are small.
I agree totally! The front end is low volume energy transfer and your exactly right!
Funny how I observed in a schematic of the very popular EAR 834P phono stages power supply how one of the caps had a 100k resistor feeding something like 47-100uf cap. I found the 834P was very dark and a bit slow sounding for my taste and I wondered why? The 12AX7 was running on a fraction of a ma. So it might have had a 30-50 volt drop. But I believe it was time constants like that that made it sound that way.
So I think even resistors one should be concern to a certain extant.
Low resistance chokes are the answer for me. Most of my power supply thinking is pretty much off the wall, so I won't go into it.
Again I couldn't agree more, DCR is where its at for dynamic slam.
Until the last few yrs I never thought about DCR or the ACR and how much do I really need!
Try to imagine that 100 ohm resistor, if that's enough.
Now image a 1 henry choke folks at a ripple frequency of 120hz its ACR is equal to 753 ohms!
Now a Dynaco ST70 has a 1H choke but it has a DCR of 60 ohms! more than the power transformer itself! Some may say better regulation, lower noise floor and so on! IMO I find it to restricting for an output stage!
But as Jay pointed out front end current demands are small typically so thats a great place for it! And better than a resistor in this case!
Thanks Jay!
