6V filaments are AC

 

the 300V comes from the 450V thru a resistor.

no need for extra power supply

I have a few PCB sets available for this amp, US $75 plus shipping.  The boards were made by PCBnet in the US, 0.093" thick with 4 Oz copper.  The set is three PCBs (Megatron amp board, KGSSHV PSU board and one Stax jack PCB).  To be clear, this is not the latest Megatron that Kevin posted on Oct 22nd.  These were made two weeks before. 

Hi,

 

Do you still have the board sets? If you do can you please check on postage to Wellington, NEW ZEALAND and advise? I would like to purchase one set.

 

Cheers!

 

Ravi

I bought a board set from jdineshk ; the power supply board is labeled version 1.1, and the amp board is labeled version .21

 

Is there a BOM that I can use with these?  A schematic that matched would be good, too.....  I've looked through this thread (albeit not exhaustively) and can't find anything I'm confident is a match.

 

Thanks.

http://gilmore.chem.northwestern.edu/megatron.pdf

I've purchased the megatron board and the power supply board from Joachim. It appears the parts that the 2SA1968 is hard to find. Can someone please suggest a source for these? Also, are there any other hard to find items for this build. Any guidance would be appreciated.

 

Don

AliExpress seems to have these with the marking 2SA1968, TO220. Are these equivalent?

Not a chance in hell that those are real.  Bdent has the real deal but they are not cheap. 

 

On the new boards these will be swapped out for STN9360's. 

/

Edited November 11, 201510 yr by JoaMat

Not a chance in hell that those are real.

Depends I bought mine from Aliexpress from a seller selling a whole bunch of jfets and rare transistors including the 1968. Purchased 10 for cheap and passed them onto a friend who has a diy BH based off headwize but needed a few because he shorted them by accident, tested the 1968's fine and has been rocking solid since with no fireworks and abnormal behaviour in the amp.

Apparently pigs can fly....   

no point in making that kind of bet imo, especially when you only need 4 and the cost of all the amplification devices in the megatron is already ridiculous

sot223 adapter boards really cheap http://www.ebay.com/itm/5pcs-Double-Side-SMD-SOT223-SOT89-to-DIP-SIP3-Adapter-PCB-Board-Converter-F63-/181328677192?pt=LH_DefaultDomain_0&hash=item2a38080948

 

Would not recommend ksa1156, though I should remember to test actual Vbr at some point

 

Tried soldering up the adapters, quick and painless. Also tested a few ksa1156 Vbr on dy294. Out of the 6 I tried, only one tested under 600V. YMMV

/

Edited November 11, 201510 yr by JoaMat

I think Kevin explored some options and originally settled on the 1968 due to its stability at .5 ma

The 2SA1486 is perfect for this role and so is the STN9360.  If you have a KSA1156 that measures well above 600V then it will work too.  Just remember the pinout difference. 

Thank you gentlemen, I will look for some STN9360's.

Thanks my passwords. Just bought some of those adapter boards for the STN9360s.

Well that substitute came at a good time, I just checked bdent and they only have 20 pieces of 1968 in stock

 

at $16 a pop

That is crazy. They were about $8.00 a year ago or so.

BTW, I am just finishing my design for the amplifier case and expect to send it to FrontPanel this week.

Very time consuming but keep triple checking everything afraid of making a 700.00 mistake

Well that substitute came at a good time, I just checked bdent and they only have 20 pieces of 1968 in stock

 

at $16 a pop

 

Well we've been using them in the KGSSHV for a few years now and the 2SA1486 would always work as a replacement too. 

Well we've been using them in the KGSSHV for a few years now and the 2SA1486 would always work as a replacement too. 

 

That's really nice to know. 

Only up to 600V though.  Don't try them in the BH... 

One funny thing I've noticed about the Megatron in office use- it picks some signals from my cell phone. Verified by disabling/enabling airplane mode.

 

Hasn't happened on anything else I've built to date

Well, finally got around finishing the design for the amplifier case and sent it to FrontPanel today.