New ST-70 Driver board from Blackburn Audio

[Burnedfingers]

Just saw a reference to a new driver board by Blackburn Audio in Chicago. The board uses a cascoded 6sn7 and a 6sn7 phase inverter.
I saw this information on diytube. The board sells for $39.95 plus shipping. I ordered one just for the heck of it.

 

[Pyre]

I am going to give one a try as well.

Are you going to put it on a ST-70 or custom amp? I am going to try it on a regular ST-70 but with a extra transformer for the filaments.

 

[Burnedfingers]

I am going to use it on a custom amplifier that I am gathering parts for. It might be a chance to use some CCS boards also

 

[Pyre]

What output tubes are you planning on using? Are a set of 6SN7's enough to drive anything bigger then a EL34? I know the Mapletree driver board used 6LS7's.

 

[Burnedfingers]

I am using 6BG6GA's in my Dynaco and I enjoy them very much so I am going to try them in the amplifier that I am going to build. I think this driver board will drive them.

 

[Pyre]

I just installed one of the new design Triode Electronic driver boards with the EF-86's last week. With a few mods it can drive just about anything.

I wish I would have seen this board before I ordered as I have lots of 6SN7's and no spare EF86's

One of the EF86's came DOA and there is nothing more disappointing then building something and having it not work. Of course I checked my wiring 4 times before moving tubes around and figuring it out. I got some EF86 locally and it works fine now.

I hope the Blackburn board works well as it would be great to have a octal option for the ST-70.

 

[Burnedfingers]

The Mapletree is another octal option for the Stereo 70. It is a good sounding driver board.

 

[Pyre]

well its an option for someone with $300

Its a fine looking board and they are about 2 miles from me down the road but $300 would buy me another St-70

 

[Burnedfingers]

Yes, an expensive driver board but I have recently purchased the parts to put together several of my own. I bought the turrets and turret tool as well. Mine will have a stainless steel polished and grained top plate unstead of the 18ga painted one that comes with the package. I may do up this design in a hand wired version. I would like to try 6SL7's in both spots I think.

 

[Pyre]

I too printed off the schematic with the intentions of wiring up my own version but when I went to buy the resistors I had trouble locating the correct values. I generally only buy PRP resistors as they say the value on them. I am colour blind therefore can not read resistor bands and my girlfriend gets really tired of me asking her what value a resistor is.

Are you planning on selling any of your version?

I have some really nice NOS 6/12SL7's that I bought to build a phono stage.

 

[bear]

Pyre,

Have you considered a digital voltmeter and bins/drawers for your resistors??

_-_-bear

 

[Pyre]

Indeed I have. With the Triode board, the resistors came unsorted in a bag so I had to test each one of them individually. I made a little set up with two clips attached to a plastic base that hooks to a digital voltmeter so I just had to drop the resistor on top of the two clips. It took a very long time though

I guess what would really speed things up is voltmeter that you do not have to change the settings to measure the different ranges. Are they called auto ranging by chance?

 

[Burnedfingers]

Finished board

 

[Burnedfingers]

another

 

[Pyre]

Hey Joe,

Looks pretty good all together. Have you got the rest of the amp built that its going on?

I ordered my board and just have to wait for it to come in now. I went with the blank board as I just bought twenty of those Russian PIO .22uf caps as everything I am building seems to need a quad of them.

I am putting the board into a ST-70 I a building that is hooked to two PAM-1's that have 12SN7/12SL7 circuits and a 3A filament transformer stuffed in them. I am going to run a filament supply for the driver board back through the octal plug.

 

[Burnedfingers]

actually I am going to try it in the Dynaco first. If you do the math the stock transformer will support this driver board. The transformer will drive the filament requirements of the dynaco and the preamplifier. The dynaco its self is 3.45 A per side and it is rated to handle the preamplifiers load of 1A per side.

 

[77seriesIII]

Have you guys been able to install the Blackburn driver boards into a modded or "normal" ST70 yet? I was wondering what anyone has thought of this mod? I've been looking at one of the ST70 designs as a possible addition in the shop to replace the temperamental radio/cd player that is currently there.

thanks

/e

 

[Burnedfingers]

Picture of board in slightly modified Dynaco stereo 70 amplifier.
Modifications to board are SDS power supply board and individual bias controls I added.

Note* This board will probably not please everyone and it is probably not going to be a favorite of SY's. The Cascode circuit is not as distortion free as other designs but does offer one the ability to use the smooth 6SN7 tubes.

The cost of this board and stuffing it is slightly under $100 as I built it and over that with some expensive caps. In my opinion the Blackburn board is sonically better than some of the current offerings of replacement boards for the stereo 70.

My personal favorite driver board is still the Mapletree board that uses a 6sj7 and 6sl7 per side or the extremely quiet 5693 and 5691 tubes.The cost of the MApletree board is in the $300. range.
I guess you get what you pay for.

Note* The Blackburn board is floated below the chassis using 4 plastic 6/32 nuts as spacers. The PC board holes were drilled out to accept 6/32 plastic nuts and screws in order to eliminate a duplicate ground if the board contacted the chassis. After the remounting the Blackburn board was noise free.

 

[Pyre]

Looks great on there!

I hope my board comes in the mail this week so I can get mine together. I have every thing stripped down and painted so far, just waiting on the post office.