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DISCLAIMER: Vacuum tube circuits work with dangerously high voltages. Do not attempt to build circuits presented on this site if you do not have the required experience and skills to work with such voltages. I assume no responsibility whatsoever for any damage caused by the usage of my circuits.

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Thursday, July 23, 2015

211 -The Next Generation- Part 4 : 801A Drives 211 Layouts

Hi!

As mentioned, there are several more 211 amplifiers in the works besides the 211 drives 211 monos. While waiting for the chassis for the 211/211 I started with the layout work of two sets of 801A drives 211 amps.




One set is meant to be used with restricted space above, so it uses more floor space but less height. The arrangement is in a square again and shown above. The 801A driver is at the back side on the right close to the input connector. The signal routes from the input through the tube to the Tango NC20 interstage transformer in the front right corner. From there to the 211 output tube in the front left corner and back to the rear through the Tango X10S output tranfsformer to the speaker connectors.




Some of the capacotors found their place on the top plate, the rest of the caps will be mounted inside along with the B+ and filament chokes and input transformer.




The separate PSU chassis follows a similar design approach as the 801A/211 amps presented a while ago : 




All Power transformers placed under covers. One large B+ transformer and two separate filament transformers for 211 and 801A.




The well proven TV Damper rectifier bridge at the front. Two caps found a little spot behind the B+transformer. All other caps and chokes will be inside.




The size of each chassis will be 380 by 380 mm. Height of the wooden frames still to be determined (approx 150mm).

The second set will have a smaller floorspace. The footprint will be square as well.




A similar layout as the first amp but only tubes, interstage and output transformer on the top.




300 * 300 mm footprint, obviously the body will have to be higher to fit all the remaining components.




The power supply layout:




Only the B+ transformer on the top along with the rectifiers.




Several tiers of components will be needed inside to fit everything in.

A comparison between the two layouts:




Stay tuned for updates as the construction of these amps progresses.

Best regards


Thomas

Monday, July 13, 2015

211 -The Next Generation- Part 3 : 211 Drives 211 PSU assembly

Hi!

After completion of the initial tests the final assembly is progressing. In this post the construction of one of the power supplies is shown.




Starting from the top with the upper plate:




In order to improve creepage distances for the high voltages present at the tube sockets, these got mounted on a separate plate which in turn is attached to the main plate with some studs.




The resistors are there to adjust the filament and heater voltages to the nominal values. Caps and chokes are mounted on a separate sub assembly and pre wired.




This is then mounted to the main assembly as the second tier.




The power transformers along with filament rectifiers and chokes are on another sub assembly




The B+ transformer in the middle at the front and the filament chokes beside it. In the back row the separate filament transformers for driver and output tube and the rectifier and caps between them. The resistors are the bleeders.

All three levels mounted and wired together:




All that is missing is the terminal with the connectors. This will be attached at the end after the PSU is inserted in the wooden housing.




The PSU in a preliminary wooden housing, feet still missing:




Next will be the assembly of the amp chassis. Stay tuned!

Best regards

Thomas



Wednesday, July 8, 2015

Tube of the Month : The 37

Hi!

When I introduced the 27 in last months post, I mentioned that it was the first in the development of a series of small signal triodes which led up to the release of the 6SN7. This month I'd like to continue with this series of tubes and introduce the first descendant, the 37.




The 37 is very similar to the 27 and basically only differs in the heater specification. Also the construction is very much the same.

It shares the same UX5 base and pinout with the 27 and has the same dimensions. The internal structures are also very similar upon first look. In fact they can be hard to distinguish visually if the printing on the glass has faded. This happened to me in the post about the 27 and I mistakenly pictured a 37 tube. try to guess which one. Of course the difference would be immediately apparent when the tube is tested. The 37 was developed with a 6.3V heater which only consumes 0.3A current. But this is already where the differences end. All other electrical parameters are very close. The amplification factor is slightly boosted to 9.2 from the 27s mu of 9. This the 37 would drop right into a circuit designed for the 27 if the heater voltage is adapted. The plate curves are also very similar.




No surprises when comparing these to actual plate curves taken from a tube sample:




Here there different 37 triodes made by RCA:




These are identical internally and only differ in the printing/engraving of the base. The RCA Cunningham has a beautifully engraved base:






This one only has the Cunningham name printed on the base, but it's made by RCA:




RCA Victor with the Nipper besides the RCA logo:




These two with engraved base seem identical:




But apparently one was produced for the military with a military number engraved on the other side:





A close up to the internals of a RCA 37 shwowing the folded heater wire in the cathode sleeve:




Philco branded 37, probably made by Sylvania:




Contrary to the RCA above the heater wire of this one is wound in helix fashion:




Close up:




A close up of the top end:




Comparison of the top sides of a RCA and a Philco:




An earlier 37 in globe shape, Cunningham branded:







This one also has a ceramic tube as insulator inside the cathode. Similar as seen on globe shape 27s. While the heater wire looped back at the top and went back into the ceramic tube, there is only one run of heater wire in this one and it is wired back to the base with the thick rod.

A close up:




View of the top with Cunningham 'C':





These little globe 37s are simply gorgeous:




Next we have a very special 37 made by Arcturus in blue glass:




This little beauty is simply stunning.




A nice shiny plate is visible through the blue glass




Close up:




Similar heater arrangement as in the globe Cunningham. A single heater wire through the center:




returned back to the base outside of the plate:




Here the heater connection from the top to the base running beside the plate can be nicely seen:




Another angle:




37 printed in orange on the glass:





These came in beautiful boxes with the observatory motif:






The boxes are still sealed and have never been opened.




These boxes are cleverly done such that the tubes can be tested without breaking the seal:




Normally the corners would get broken to insert the tube into a test socket. But these boxes even had the corners intact so they are really untouched. To take photos I had to break the seal of one:




But it was worth it to get these foots taken in the moon light:




tube at the lake front:




Moon light reflecting in the water behind the tube:



Another shot:




The 37 has one drawback however. The heater glow is very dull and barely visible even in the dark, here a ST shape 37 in operation:




Close up:





The heater at the bottom end:





The globe version even glows less:





It takes a long exposure time on the camera and a dark environment to make the glow visible:




Even less light comes through the blue glass of the Arcturus:




So not a tube for glow fetishists. But who could resist the beauty of this cool Arcturus master piece ?

Best regards

Thomas