diytube.com

I see that we have a new ST-70 driver board offering here in the Chicago area.
Matt Ihnen has started a new company: Blackburnaudio.com
http://www.blackburnaudio.com/index.html

His first product offering is a 6SN7GT based driver board for the ST-70.
http://www.blackburnaudio.com/Dynaco.html

This is the first octal tube driver board I have seen for the ST-70.
This triode board will require the new TriodeElectronics ST-70 transformer, due to the higher filament current for these tubes.

A bare board is listed at $39.95
http://www.blackburnaudio.com/products.html

G. Beat
Elmhurst, IL

Mapletree has had an octal "Special Red" driver board for the ST70 fo a few years. Uses 6sj7's and 6SL7's.
About half way down the page:

http://hollowstate.netfirms.com/

http://hollowstate.netfirms.com/SRinsta ... ctions.pdf

I've used it in a build and couldn't be more pleased
I've posted the pics a while back.

Jeff Davison

Mapletree has an octal "Special Red" driver board for the Dynaco ST70

Jeff -

Thanks for that link. I was not aware of this offering.
I see that the Mapletree board uses 4 sockets and turret point wiring (like some traditional guitar amplifier designs) underneath the board.
The Blackburn PCB is 0.062 Blue FR4 with 2oz copper
Extra pads are there to mount large coupling capacitors.
You can install 2W to 5W resistors to permit the board to support the 6BX7 or 6BL7 tubes - BUT you will need to have a transformer to support the required 1.5 Amps!

g. beat

Blackburn Audio will also supply you with the PBC template if you wish to make your own board, he even has the schematic if you want to point wire your own board, that is top notch as he understands we are DIY!

Sal

Jeff,

I also have a MApletree driver board that I am quite pleased with. I would suggest not purchasing the tube package for the additional $50 however.

Just purchased the Blackburn board and I am looking forward to getting it.

I bought mine about a year and a half ago without the tubes, for the same price Dr Lloyd put in Auricaps for the couplers. Currently it's using a couple of 5693's and a couple of ECC35's.... glorious... driving a quad of 6550 Blackplates circa '58.

JD

burnedfingers wrote:Jeff,

I also have a MApletree driver board that I am quite pleased with. I would suggest not purchasing the tube package for the additional $50 however.

Just purchased the Blackburn board and I am looking forward to getting it.

I'm running 5693's and 5691's with 6BG6GA output tubes and it sounds good. I do believe the Blackburn board is going to smoke it.

I received the board today. Now to update the schematic with part designations.

When ordering parts be sure to include the two 18K resistors which are missing from the parts list.

I added the 18k resistors to the parts list, not quite sure how they got left out. Next time please contact me to let me know about any errors or omissions in the instructions so I can correct them for others. If I don't know about a mistake there is nothing I can do to correct it. Thanks.

-Matt

This triode board will require the new TriodeElectronics ST-70 transformer, due to the higher filament current for these tubes.


Actually I disagree with the above statement. The dynaco was designed to provide the heater requirements of the stock circuit which is 3.45 A per side. In addition the dynaco was designed to also provide the requirements of the preamplifier that plugs into the front of the amplifier via the two octal sockets. This additional capability will allow for the difference between the current draw of the 7199 tubes and the 6sn7 tubes.

The fact that the transformer runs at around 113 degrees should not be considered as a scare factor. THe dynaco transformers have been running since the conception in the late 50's and I have yet to see one burn out due to the higher than ambient temperature.

You may be correct, but you have to be extra cautious when you sell boards that will push the power transformer to its limits because the last thing you want is for a customers PT to fry and have them claim that you are responsible.

Dynaco did allow headroom on the filaments for the preamplifier and in reality you should be able to run my board with a stock PT without causing any damage, it would be within spec for the ratings Dynaco claimed. However when people install a new board and all the sudden their PT is hot enough to fry an egg they usually become very concerned. Then you have a lot of emails from people wanting to know if their PT is okay. I had to deal with this all the time with the PA774's when working for Triode.

If anyone wants to give one of my boards the old smoke test with an original PT be my guest and I would be interested to hear the results as I have not run this board for any extended amount of time with an original PT.

-Matt

If anyone wants to give one of my boards the old smoke test with an original PT be my guest and I would be interested to hear the results as I have not run this board for any extended amount of time with an original PT.

I finally ordered the parts to put it together and will do so shortly in one of my units. I will use the original power transformer and advise of the results.

Note* It is perfectly normal for a transformer to run warm. I do not consider 113-115 degrees as anything to worry about otherwise I would not have posted. If people feel the need to replace a perfectly good transformer then by all means do so if it makes you happy. Another check of the capabilities of the transformer would be to monitor the heater voltage to see if it changes when driving a slightly heavier load. If it does then I would highly recommend it be replaced. I do believe they will find out as I have that the heater voltage does not change.

Dynaco did allow headroom on the filaments for the preamplifier and in reality you should be able to run my board with a stock PT without causing any damage, it would be within spec for the ratings Dynaco claimed

*****

On page 2 of the Dynaco manual there is a specification which states the sockets on the front provide 1 A per side.

I can see the need to CYA when selling an aftermarket product. At some point reality should be brought into the picture. Dynaco surely would not have designed a product that would cause a rush of law suits. In obtaining the transformer class rating the temperature is surely a factor. I'm sure the transformer is within specification since they have obtained a UL rating.

Dynaco surely would not have designed a product that would cause a rush of law suits.

Please ! People in the 50's and 60's didn't sue like people
do today ... hot coffee in the lap, kid wearing soft plastic shoes
getting foot caught in the escalator, etc. Product liability
lawsuits were virtually unheard of back then.

Blackburn Audio wrote:If anyone wants to give one of my boards the old smoke test with an original PT be my guest and I would be interested to hear the results as I have not run this board for any extended amount of time with an original PT.

-Matt

I have a couple of ST-70's I can try your board on, you can send me one for evaluation and I can take before and after temperature measurements of the transformer. I will send back the board after the testing is done.

Sal Brisindi