Hello all, after finding this site while googling information on my Dyna MK IIIs a year ago and lurking occasionally since then I decided to join. A little background, I'm not a real do-it-yourselfer as most of you are. I have built kits off and on since the mid 70's. My first stereo consisted of a Dynaco ST 400, Pat 5 into JBL L65 Jubals I bought new in 1975. I have those Jubals in my system to this day, though I own and have owned other good speakers over the years including Martin Logan CLS's and various B7W's. The kits I built up were the aforementioned Dynaco ST400 and Pat 5, an early 80's Heathkit tuner, the Van Alstine Super Pas III, Dyna Mk IIIs and a Heathkit knotmeter for my sailboat.
I married in 1991 and moved from Hawaii to Montana. I took all my hi fi equipment with me, but being married changes things, and slowly as my amps and other gear died piece by piece it was put in a closet until all that was left was the home entertainment system that was all the rage in the early 2000's. About a year ago my best friend from LA and I began pining for the old two channel systems that gave us so much listening pleasure over the years. I decided to get my whole system back up and running piece by piece.
First item on my list was my Mc225 power amp. I sent it back to Yves Beauvais for a total restoration. The Van Alstine Super Pas 3 I built in 1990 still worked fine as did my old Kyocera CD player, so for the first time in over a decade I was back in business. All I have for speakers right now are those 75 vintage L-65s and a nice pair of B&W DM 2000s from the late 80s. I traded in my CLS's for part of my home entertainment system around 2009. The Mac sounds wonderful through both speakers. The JBLs and B&W's are like chocolate-strawberry, just different flavors but both are great.
Over the past year I have fixed up are just checked out and played; my early 80's Yamaha CR2020 receiver, Conrad Johnson PV2a pre amp, the Super Pas III pre amp, my Dyna Mark III monoblocks with the SDS power supply mod and new tubes, two turntables a Sonograph with Sumiko MMT tonearm and Van Alstine's Longhorn Grado cartridge and a B&O Beogramm 2002, Hafler DH 220 and Nakamichi tape deck.
Here's a pic of some of it set up in my den...
I actually joined to ask for advise on the best of the commercially available driver boards for my MK III amps, but I'll do that on another thread.
John
I married in 1991 and moved from Hawaii to Montana. I took all my hi fi equipment with me, but being married changes things, and slowly as my amps and other gear died piece by piece it was put in a closet until all that was left was the home entertainment system that was all the rage in the early 2000's. About a year ago my best friend from LA and I began pining for the old two channel systems that gave us so much listening pleasure over the years. I decided to get my whole system back up and running piece by piece.
First item on my list was my Mc225 power amp. I sent it back to Yves Beauvais for a total restoration. The Van Alstine Super Pas 3 I built in 1990 still worked fine as did my old Kyocera CD player, so for the first time in over a decade I was back in business. All I have for speakers right now are those 75 vintage L-65s and a nice pair of B&W DM 2000s from the late 80s. I traded in my CLS's for part of my home entertainment system around 2009. The Mac sounds wonderful through both speakers. The JBLs and B&W's are like chocolate-strawberry, just different flavors but both are great.
Over the past year I have fixed up are just checked out and played; my early 80's Yamaha CR2020 receiver, Conrad Johnson PV2a pre amp, the Super Pas III pre amp, my Dyna Mark III monoblocks with the SDS power supply mod and new tubes, two turntables a Sonograph with Sumiko MMT tonearm and Van Alstine's Longhorn Grado cartridge and a B&O Beogramm 2002, Hafler DH 220 and Nakamichi tape deck.
Here's a pic of some of it set up in my den...
I actually joined to ask for advise on the best of the commercially available driver boards for my MK III amps, but I'll do that on another thread.
John
Welcome to diyAudio JohnThat's some impressive kit you mention there.
Thanks guys, I guess it's all relative. Not very impressive compared to what many of you have built from your own designs, and like all humans, I'm always yearning for something more.
Anyway the subject of my question are my two MK III amps. You guys will probably kick me off the site for this, but I actually traded my working perfectly Conrad Johnson MV75 straight across for these two amps. The CJ power amp was impressive to look at but seemed a bit warm and mushy compared to the MK IIIs which were tighter and more airy. Not a wise decision from a money standpoint but I liked the sound better. Anyway I used them to drive the difficult load of my ML CLSs for years and for years they ate tubes until I quit and switched over to the Hafler DH220.
As I posted above I pulled the old MK IIIs out and modded them with the SDS cap mod. They work fine and sound great, but run pretty hot. My live voltage is high at 123 volts out of the wall, the voltages off the #3 and 4 pins are correspondingly high at + and - 564 volts, the manual calls for 475. I set the bias at an even 1.50 volts rather than the 1.56 called for in the manual. So I have a few questions:
1) Does that B+ voltage drop if I bias them lower, say 1.40 volts?
2) Does it drop if I Variac the wall voltage down to 117 volts?
3) I assume running it that high is harmful to the tubes, GE 6550 btw, is that true?
4) Somebody on another site recommended I swap the GZ34 rectifier for a 5U4GB to drop that voltage. He noted that I would have to add a 25 s delay to the filament to prevent it from high voltage spiking. Is that a good idea?
5) Finally, I want to upgrade from the stock driver board, there are quite a few kits available for this, the Poseidon, the Triode, Tubes 4 Hifi, Kennedy, others. Any opinions on these boards?
John, I have to admit I'm more of a solid state person and so I think probably best if you post those questions over in the Tube/Valve forum where many far more knowledgeable than I in valves would have a better idea.
Tubes / Valves - diyAudio
Just copy and paste your relevant text over to a new thread. I don't think the variac is a good idea tbh, its messy and will significantly raise the impedance of the mains supply. I would try anything and everything before going down that route. Higher supply voltages could be putting any reservoir caps up to close to their maximum voltage ratings.
Also for a given bias current in a valve, any increase in plate voltage will see quite a large rise in plate dissipation. If you try and loose voltage with a rectifier change then that lost voltage is dissipated as excess heat assuming the current draw of the amp remains the same.
See what the thermionic guys think
Tubes / Valves - diyAudio
Just copy and paste your relevant text over to a new thread. I don't think the variac is a good idea tbh, its messy and will significantly raise the impedance of the mains supply. I would try anything and everything before going down that route. Higher supply voltages could be putting any reservoir caps up to close to their maximum voltage ratings.
Also for a given bias current in a valve, any increase in plate voltage will see quite a large rise in plate dissipation. If you try and loose voltage with a rectifier change then that lost voltage is dissipated as excess heat assuming the current draw of the amp remains the same.
See what the thermionic guys think
John, I have to admit I'm more of a solid state person and so I think probably best if you post those questions over in the Tube/Valve forum where many far more knowledgeable than I in valves would have a better idea.
Tubes / Valves - diyAudio
Just copy and paste your relevant text over to a new thread. I don't think the variac is a good idea tbh, its messy and will significantly raise the impedance of the mains supply. I would try anything and everything before going down that route. Higher supply voltages could be putting any reservoir caps up to close to their maximum voltage ratings.
Also for a given bias current in a valve, any increase in plate voltage will see quite a large rise in plate dissipation. If you try and loose voltage with a rectifier change then that lost voltage is dissipated as excess heat assuming the current draw of the amp remains the same.
See what the thermionic guys think
Isn't this the tube/valve section?
Lol, so it is. Not the first time I've done that either, I must be more careful
I think the thread title is what did it.
I can change the title of this if you wish.
Probably best not to have two threads on the same question or if you want to rehash it completely then this can deleted.
Back in a bit
Yes please change it, that would be great. Anything about Mark III driver boards, or just a general question on modding a MK III.
First, let me tell you how insanely jealous I am- you live in Paradise. We were in Butte for a year and absolutely fell in love with MT. I would move back there in a second.
Second, the C-J designs are... well... not great. You did fine changing over.
Third, don't sweat the operating conditions too much. Your speakers aren't exactly resistive loads. You could run just fine at an elevated voltage if you decrease the idle current (as you did). The worry I'd have is the heater voltages- are they similarly out of the nominal 6.3V? If so, the way to fix everything in one shot will involve adding a buck transformer to reduce the effective primary voltage. Measure the heater voltages, and if they're higher than 6.5V from end to end of the heaters, we can walk you through how to do this.
Second, the C-J designs are... well... not great. You did fine changing over.
Third, don't sweat the operating conditions too much. Your speakers aren't exactly resistive loads. You could run just fine at an elevated voltage if you decrease the idle current (as you did). The worry I'd have is the heater voltages- are they similarly out of the nominal 6.3V? If so, the way to fix everything in one shot will involve adding a buck transformer to reduce the effective primary voltage. Measure the heater voltages, and if they're higher than 6.5V from end to end of the heaters, we can walk you through how to do this.
Sorry it took so long, my voltmeter died and I don't get into town that often. I just got a new one yesterday and took the following measurments:
Bias set at 1.50 volts
6550 Tube socket:
Pin 1 1.54 volts
Pin 3 492 volts
Pin 4 495 volts
Pin 5 +53 volts
Pin 6 -53 volts
Pin 8 1.56 volts
Pin 2 to pin 7 6.7 volts AC
It seems biasing it down a bit helped lower my B+ voltage which was sky high a year ago at 575 volts, now it's just a little high (495 v). On the other hand, you were right to worry about those heater voltages, that 6.7 voltage seems bad, what do you think?
As a further note, I am going to rebuild the amps further as follows:
1) Pull out original driver and replace with Tubes 4 Hifi or other driver.
2) Leave new SDS power supply intact.
3) remove all wiring and original tube sockets, except the hard wires out of the original transformers.
4) New power cord.
5) new speaker terminals.
6) New input jack.
7) Dual bias circuit.
8) Pentode/Triode switch.
I also plan on buying Variac off ebay to plug a high quality power strip into. Then all my other equipment will be running off 117 volts or whatever I set it at.
1) Pull out original driver and replace with Tubes 4 Hifi or other driver.
2) Leave new SDS power supply intact.
3) remove all wiring and original tube sockets, except the hard wires out of the original transformers.
4) New power cord.
5) new speaker terminals.
6) New input jack.
7) Dual bias circuit.
8) Pentode/Triode switch.
I also plan on buying Variac off ebay to plug a high quality power strip into. Then all my other equipment will be running off 117 volts or whatever I set it at.
I would be running a pair of MK IIIs, CD player, turntable and Super Pas 3 preamp, would a 5 amp unit be enough? The Mark IIIs draw a little over an amp each.
Yes, too high. I'll try to sketch out a buck transformer connection for you. You'll just need a cheap 12V transformer for that.
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