Dynaco Tubes4HiFi VTA SP-6 Preamp build thread.

[Guest David H]

I have always been a fan of Dynaco products and their founder David Hafler, over the past few years I have found some upgrades for my Dynaco's worth talking about. First and foremost is Vacuum Tube Audio's Dynaco 70 upgrade board. I purchase this upgrade and found it to be far superior to any of my other Dynaco upgrades to date. To my ears, the VTA upgrade simply breathes new life into this already good but outdated Dynaco design. Which brings me to this build thread for the Tubes4HiFi VTA SP-6 Preamp.

Kit contents: (1) Circuit board which includes: line stage, phono stage, and power supply neatly organised on a single board.

(2) Well detailed layout with referance numbers to the parts list.

(3) Easy to read schemaitic, also labeled with reference numbers to the parts list.

(4) Step by step instrucion manual is a little vague, so some experiance is required, or follow this post.

Now that we have gone over the Kit I am going to get on to the build. I am still waiting for a few parts, like transformer and chassis so this build will be spread over a week or two, so stay tuned.

Kit photo

[Guest David H]

Attached is a pic of the bare board and layout.

[Guest " "]

super......I have 4 dynaco mark VI's....two complete and fully functional...two complete and unbuilt kits in original boxes.

[Guest David H]

Here I am showing the baged parts, most of the parts are separated to simplify the build, I like to go the extra mile and separate all of the parts in labled trays. Then I check against my parts list to insure I have all the parts. Turns out I had 1 extra resistor, if I had not verified the counts I would have spent alot of time double checking to find where I made my mistake. Overall this proceedure will save time locating parts, and will reduce the risk of installing parts in inapropriate locations.

[Guest David H]

Official step one.Install and solder the tube sockets in appropriate locations. What the instructions neglect to mention is find the top of the circuit board then install the parts. I have been in contact with Roy Motram at www.tubes4hifi.com to resolve questions and simplify this build. Roy is great to deal with and answers my emails promptly. He has already made a few revisions based on my input to simplify the build for beginner like myself.

My revised step one is locate the B+ symbol on the circuit board. this is the top of the board. Now that you have located the top of the board stuff the tube sockets and fuse holder. The B+ is very small located next to the 12x4 tube socket.

I almost forgot, It is absolutely essential to play great Jazz while building the SP-6. What happens is: If the Jazz is good enough it enters your ears and literally tranfers good vibes into the electrical components you are installing by way of solder flux an physical contact.

[Guest David H]

Step 2 is to install the resistors and diodes, as I stated earlier, separating the parts make this build easier. The parts list starts with resistors so I simply installed the parts in order as listed, except the large capacitors I will install last to minimize obstruction, and allow the best board access.

I am not going to show step by step for each resisitor batch, as it would lenthen a reasonably simple build.

RESISTOR COLORS FOR VTA SP6

R100-103 R200-204_220O 1% Red, red, black, black, brown.
R205-206_680O 1% Blue, gray, black, black, brown.
R104-105_910O 1% White, brown, black, black, brown.
R106_3.3kO 1% Orange, orange, black, brown, brown.
R107_4.7kO 1% Yellow, violet, black, brown, brown.
R108_6.8kO 1% Blue, gray, black, brown, brown.
R109_10kO 1% Brown, black, black, red, brown.
R110_47kO 1% Yellow, violet, black, red, brown.
R401_51kO 1% Green, brown, black, red, brown.
R111-113, R402,403_150kO 1% Brown, green, black, orange, brown.
R114,115,207,208_330kO 1% Orange, orange, black, orange, brown.
1W R303-220O 1% Red, red, black, black, brown.
1W R301,302_1.5kO 1% Brown, green, black, brown, brown.
1W R209-4.7kO 1% Yellow, violet, black, brown, brown.
1W R304-6.8kO 1% Blue, gray, black, brown, brown.
3W R304-0.1O 1% Black, brown, black, silver, brown. NOTE GREEN

This resistor info might help.

[Guest David H]

Here's a photo after a few batches of resistors are installed. Notice the high quality resistors used near the tube sockes, this is the passive RIAA ( Recording Industry Association of America) phono section.

[Guest David H]

Step 3 is to install the capacitors. This task was problematic for me as I had no Idea how to read the orange drop values. Fortunately Roy Mottram anticipated this scenario and listed the part numbers as well as the values. I realize orange drop capacitors are a respected good quality component, but my preferance is film and foil. So I checked my stock of capacitors and I had a few .10uf Dayton film and foil bypass caps on hand so replaced as many orange drops as possible and ordered the ones I did not have from www.partsexpress.com.

Here is where I need your help, The output coupling caps are .33uf Solens Roy informed me that I could replace them with a larger value, which would pass lower frequencies, but they may not fit on the board. My thought was to use multiple sets of output coupling caps on a rotary swithch and be able to select the ones I like best. I have plenty of room in the chassis I have coming to add a cap board.

What cap values do you think would work well, for a 2 tube gain stage?

What reasonably priced caps would you suggest? Russian PIO, Sonicaps, Kimber, dayton, etc. No need to mention expensive V-Caps etc, not going to spend more on caps than the rest of the kit.

Here is a pic of the completed board.

[Guest David H]

Step 4: The last step in board assembly is to install the power jumper wire. I chose to install this lead under the board to keep things neat.

[Speedball]

______________

[Guest David H]

I modified this layout by adding capacitor values and info, to ease assembly for first timers that would like to build this kit.

VTA_SP6_edit_dh.pdf

[Guest David H]

Here is the original document

VTA_SP6c_layout.pdf

[Guest David H]

Thats all I have for now, as I progress I will add additional info. If you would like additional info or would like to read a few reviews on the preamp see http://www.tubes4hifi.com/pre3.htm

[Guest David H]

super......I have 4 dynaco mark VI's....two complete and fully functional...two complete and unbuilt kits in original boxes.

Cool, I will be expecting a build thread. BTW I'm jealous.

[fini]

Nice Job!

[mikebse2a3]

Nice Thread GotHover! Like you I also have alot of respect for David Hafler's designs and especially from a bang per $ aspect.

I can't tell from your photos but just in case and for anyone that might be building these or similar kits one important TIP I would give is make sure the resistor bodies are located physically far enough off the circuit board so as not to make contact with any copper circuit traces that run under them as well as the resistors's bodies physically not in contact with each other as well.

mike tn

[Guest David H]

Thanks Mike, I was not aware of touching the traces being an issue, but I checked and all look ok except 2 resisters were touching.

I also noticed I put a film and foil cap in the power supply circuit, so I pulled it and put the orange drop back in.... duh...[:S]

[mikebse2a3]

Your welcome and don't feel bad I've seen this cause problems even with very experienced manufactures most recently in a McIntosh MC2000. It can lead to a malfunctioning circuit, intermitent problems/failures and if for any reason a problem developes that overheats a resistor it is much less likely to damage the circuit board.

mike tn

[mark1101]

I'm running a Bob Latino VTA-120 (60 wpc dynaco clone) with the VTA driver board. The thing has proven to be bulletproof and uses 12AT7 tubes which are easy to find in NOS for reasonable prices. I have been really happy with the performance especially for what I paid.

[Guest David H]

I have always wanted to try the Dynaco ST-120 VTA. Just not sure if I am ready to build it.