|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
184.188.184.170
In Reply to: RE: The Monster Amp posted by Sherwood Forest on October 13, 2014 at 08:08:41
Here's the safety circuit. It monitors the bias voltage, and it shuts off the plate transformer and drains the caps should any problems occur. It also serves as a soft-start. It's the only place in the amp to use solid state circuitry.
Follow Ups:
This is a mockup of the amp, with top plate to be made by front panel express. This is a KT-90 (or equivalent) amp, uses HK Citation II OPTs, Lundahl interstage transformers, and has all of its metering functions built in. It has 6 modes of operation; Triode, Pentode, & Ultralinear in either SE or PP.
Here's the case for the amp. Solid oak, finger joined, and then lined with copper foil for electrostatic shielding. The foil is overlapped in 4" strips, then the edges are soldered together to provide mechanical strength as well as low resistance.
So here's the story:
The power supply uses 9 rectifers (6AU4 or 6AX4, 8 for the HV+ and one for the bias. The bias supply is regulated by an OA3. There are 4 OD3 tubes in there, they provide two 300v regulated sources for the screen grids, when the amp is in pentode mode.
The amp has knob selectable operating modes; Ultralinear, Pentode, and Triode connected, either in SE or PP.
The HV+ supplies 550VDC at 600ma. The outputs are nominally KT-90s, but can take just about any standard based octal tube. It can run either 2 or 4 tubes per channel, and can output over 100WPC in pentode or UL modes.
The metering is quite extensive, you cannot only measure bias, you can also measure output at the various driver stages, as well as the power output to the speakers. The meter circuits use two tubes for voltage regulation and reference voltage, and can be self-calibrated.
All pots are either 10-turn precision wirewounds, or in the case of the adjustable feedback and volume controls, stepped attenuators (ladder and series type)
The interstage transformers are Lundahl 1660, and the outputs HK Cit II. (thanks to Jim McShane!). The driver tubes are 6SN7, but with socket adapters, can make use of 6CG7 and lots of other twin triodes.
The power supply includes a standby switch, as well as an hour meter, which is very useful for knowing real numbers about tube life.
Most of the heavy design, SPICE modeling, etc. was done by a very well known and respected analog engineer, I am mostly responsible for the topology choices and the build.
All wiring is mil-spec silver plated copper w/ Teflon jacket. Octal sockets are NOS Amphenol ceramics
Please let me know what you think.
I love ST shouldered voltage regulators and this hobby IS about having fun. One ST shouldered VR beats a flush of zeners any day. The flexibility lends you the ability to change topology with music regimens... if needed.
The Mind has No Firewall~ U.S. Army War College.
Very nice build! Did you use the Front Panel Express program to design the top plate or some other program? This looks like an experiementer's/tweaker's delight with so many knobs.
Hi,
Yes I designed the entire thing in the FPE program. In fact, there's nothing I used that wasn't standard as a part of their program. I have yet to experiment with importing HPGL graphics, though I may try to sneak a logo in there. The darn top plate is already pushing $850 with all the engraving and weird holes I am using.
Yes, this thing is a tweaker's delight! I am certainly the kind of person to do a lot of tube rolling, and experimentation, and I really like the fact that this design allows for that. The built in metering is, in my opinion, the key because it allows you to try new things without taking the cover off and putting one hand in your pocket as you probe around. I could swap the 6SN7 for a 6DJ8 (using a socket adapter) and be able to compare the driver voltage output, for example, all without external metering.
One cool thing is that the 10-turn dial counters allow you some degree of repeatability; you can know exactly where your bias points were at on each tube visually, so you can try different arrangements, but go back one you tried earlier with relatively little effort. The correlation between the knob's reading and the bias reading on the meter allows you to make relative observations about how much bias you need to get a tube to conduct X milliamps. It doesn't give actual usable figures, but if one tube requires the bias knob to be at 850 to reach 50ma current, and another one requires the knob to be at 675, then you can make observations about how well matched for cathode current tubes are. This will also be useful as tubes age, you can see what dial setting is required to maintain bias compared to when the tubes were new.
Thanks for the input. Nice folks like you are more than welcome to see the schematic, just PM me if interested.
Just got my test cuttings from Front Panel Express today! Things are looking quite good. I'll upload the templates in case anyone wants to use them.
This is a standard Amphenol ceramic socket, NOS, but I think it is exactly the same dimensions as the phenolic or bakelite ones. Anyway, I make a hole that accomplishes 3 things! First, it allows you to use nice, thick, 4mm aluminum, which is otherwise impossible with this socket. Secondly, it does away with the metal bracket and the screws requiring only the snap spring to mount it, and lastly, it allows the socket to sit just slightly proud of the top, which is how you want it.
Here's from the top
The underside. As you can see, only the spring clip is needed, and let me tell you it is SOLID. That sucker wont budge at all.
Here's the hole, you can see how it works. The socket is recessed into a larger hole, which is stacked on top of smaller hole with a key.
Doesn't look like I can't upload a front panel express file here, so I'll link it to dropbox for you!
https://www.dropbox.com/s/5yjj0rtobq0h6zm/Amphenol_Octal_Screwless_4mm-plate.fpd?dl=0
Thanks very much for the FPE drawing. I assume that I can create a macro from the two cavity drawings (circle 32.5 mm and cutout EAO-Serie-61F.dxf), but I believe I need Cutout drawing EAO-Serie-61F.dxf to add the cavity with the tab.
Hi,
I am glad I put something up here that somebody found useful. Let me know if you need anything from me. That notched hole, the one you are missing, I can't remember if that came with the program or if I downloaded a supplemental pack. Either way, it was obtained from FPE. I took that one notched hole, scaled it, and then added the other hole on top. It might just be that you have an old version of the program?
To make the thing a macro, you just select all, then edit-> grouping, once it's grouped, you can save as a macro. Still haven't figured out how to just export macros.
Anyway, I'll play around tonight and see if I can get it exported. I also have a template now for the Electroswitch rotary knobs, I'll link that up later.
Cheers!
I think you must be correct that the EAO-Serie-61F.dxf file probably came from FPE. I will have to look for it if I decide to mount the tube sockets that way in the future. Right now I have made macros for 9 pin and 8 pin sockets that use a saddle to mount them that also include vent holes around the socket. It certainly makes it convenient to add a bunch of tube socket holes to a panel quickley and accurately. I can't find a way to export macros either.
Here's the hole template for the ETI MW22B-10 precision 10 turn wirewounds. This template also has a key hole on the top that's for Litton 10-turn dial counter knobs, but may work with others. At any rate, you can delete the top-side keyhole if you want, it's only for the dial counter.
This arrangement works well in 4mm plate. Like the octal socket hole, this is a multi-diameter hole with a key. The pot countersinks from the back, goes in far enough to get the key in the hole, but allows the strain of the nut to be placed on the shoulder of the brass shaft collar, rather than on the plastic, which might break it. All in all, this hole came out perfect and needs no revisions at all for 4mm plate.
https://www.dropbox.com/s/mpgiiafr2ab1rgh/2014-10-14%2000.54.00.jpg?dl=0
I should have also mentioned that while the hole is perfect, you must omit the lock washer due to the thickness of the 4mm plate if you wish to use this particular dial counter. Otherwise, it probably wouldn't be an issue, but in any case works just fine without the lock washer (use loctite).
Just got the stepped attenuators from Khozmo today. They seem fantastic. All three were custom made; a 50K ladder and two 1K series. The ladder is for the volume, the two 1Ks are for the adjustable feedback circuit.
I'm taking measurements now, they're a little odd, but I think they make sense. I'll report back when I better understand them so as not to go off half-cocked.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: