mwl168

I believe that 2SC4686A would be good substitute for Q8-10, Q13-15? 2SC4686A is a 1200V device available at BDent and much less expensive than 2SC3675 but lower hFE. If you are willing to take the risk, 2SC4686A is also available at Utsource and the last batch I bought from Utsource tested similar to the ones I got from BDent. Be warned that Utsource sells mix of genuine and fake parts. Based on suggestions from someone very knowledgeable here, I plan to use 2SC3675 in the active batteries (need high hFE), 2SC4686A in the output current source and FJPF2145 for all other places to substitute for 2SC3675 in the T2.

Hi JoaMat: Have you considered experimenting with STP03D200 in the active batteries to replace the 2SC3675? It's a 2KV Darlington transistor with hFE > 200. This part was actually mentioned in the DIY T2 thread long time ago. It's a current production part available from Mouser, etc. and expensive (> $6 US) but still cheaper than 2SC3675 and much easier to source.

Based on my experience, 24vac and 60va transformer is the minimum for 24VDC rails to supply a pair of CFA boards. I use two 100va transformers for my dual mono, balanced CFA amp running 30VDC rails. For GRLV, I did match the 4 resistors that determine the regulated voltage. No need for 5 decimal precision though. The LT1021 voltage reference has its own tolerance as well.

The chassis you showed should work if you can fit everything in. It looks to me a similar chassis to the one I am using for mine. I posted photos of it when I had the PSU built in. Mine is a balanced amp. Maybe consider moving this discussion to the thread dedicated to the dynamic CFA build.

Remind us are you picking a chassis for a singll-ended or balanced build? PSU in the same chassis or separate chassis?

Received confirmation from the fab house that our orders are in production (each distinct Gerber file is considered one order). I've opted for boards to be shipped to me in batches when they are ready so we are not all held up by the partially assemble GRHV boards which will take longer than the rest of the PCBs.

Love the red telephone - direct line to the White House?

Happy Birthday! 🎂

Judging by the photo you should definitely see output voltage change as you adjust the pots. If not, I would first check to see if the pins of the pot are soldered in correctly - is it possible you soldered pin 1 and 3 of the pots to the fixed resistor positions?

What tonearm is that? Looks like a triplanar but not quite...

Table updated. This GB is now officially closed. Submitted latest version Gerber files and corresponding final quantities to the fab house. Will update with ETA of manufactured boards when I receive confirmation.

1. I experimented with different voltage rails PSU with my build. Cannot say I heard a real difference but my CFA is balanced, not single ended. 2. The heatsink size you are planning for should be fine. You do need to pay attention to heatsinking the PSU as well. This amp draws significant current from the PSU.

Table updated. Received all but one payments. I have proceeded to contact PCBnet to place our order.

Table updated.

I don't see any reason not as long as they fit the board physically and the voltage rating is within spec.

Table updated.

Table updated.

That's great news! Are you able to get rid of the hum too? Don't understand your question but all major tube manufacturers back in the days, RCA, GE, Sylvania, etc.,made 6SN7 GTA\GTB tubes. Looks to me most, if not all, current production 6SN7 tubes are of the GTA\GTB variant. Just check the plate voltage and dissipation ratings in the datasheet. JimL picked fairly conservative operating points for the output tubes of the SRX Plus but I would personally want the plate voltage rating of the tube to be 20% above the B+.

^ that photo gives me hernia...

Table updated.

We are ready to collect payments from all GB participants and get the boards ordered. Here are the quotes (in USD) based on the quantities we have: Mini T2: $22 (per pair) GRHVxxx partially assembled: $54 GRHVxxx bare board: $4.5 GRLV78: $4.5 GRLV79: $4.5 PSU Main board: $8 The GRHVxxx bare board quote went up $0.5 due to the reduced quantity. The mini T2, PSU main and partially assembled GRHV boards all went down slightly. I have updated the table in the first post of this thread with every participant’s total payment for the boards. This payment does not include the shipping cost from me to you. Please PayPal me your payment to by end of day Wednesday, April 8. I will place the order with the fab house when I received all payments. Add 2.9% if you are in US and 4.4% if you are outside US if you prefer not to use PayPal Gift. Please remember to include your HeadCase ID and shipping address in the PayPal payment note. It should take about 2 weeks for the boards to be manufactured and delivered to me. I will then package and send the boards to you. I will request for shipping cost from me to you via PM prior to sending you the package.

Table updated.

I did exactly that - built a universal PSU for KGSSHV, Carbon, GG, BH and the CFA. IME, GG and BH are rather similar. Have not heard a full DIY T2 but building one PSU, a BH and a Carbon will not come close to what it costs to build a T2.

me think that God would have given us three hands if we were meant to do SMD soldering.

Waiting for the final quotes from the fab house. Once the quotes are in I will update the table with the total board payment for each participant. At the point I will be collecting payments from all participants using PayPal and PayPal only. More details to follow in a few days. You need to be specific about which boards you want and how many and whether you want the partially assembled or bare GRHVxxx boards. Read through this thread if the difference isn't clear to you - the information is all here - so you can make the right decision for yourself.