Blueman2

Thanks Jim! Especially for pointing out the need for 2 6.3v windings. Most transformers have that, but one I was going to buy did not, so you saved me from wasting time/money on that one. And to confirm, a 1000vct is OK, right? Just gives more headroom for brownouts (which we sometimes get).

JimL, Thanks again for sharing this and for the great article in AudioXpress (I subscribed for a year just for your series of 2 articles!). I had a couple questions as I started to bring parts together. - For the transformer, is the 5v tap needed? I can more easily find 800vct and 6.3v taps, but more rarely do they also include 5v. - Is a larger cvt OK? I found a very nice 950vct 140ma transformer with a single 6.3v 2A tap. Would that work OK? - in your image above, I see a LOT of big iron in that thing! Big grey box to left certainly looks like a transformer. What about the darker grey smaller box and the 2 beige boxes to the right of those? and the black box to far right? Finally, Jim, is there a simpler power supply I can build for your SRX-plus amp? Something perhaps smaller and solid state only? Just curious what my options are for power supplies. Thanks for helping a newbie come up to speed. Blueman2

Doh! I had that schematic but did not understand what to do with it. So I need to breadboard D101-106, C101-106, R101-105, and the back-to-back 100V zeners. - I can either leave out C108 or put it before R104, right? - can I leave out C107 and R103 since I only want Pro bias Thanks!!

Put me down for 2 of Amp and 2 of PSU. For the PSU, I lean towards whatever is a simpler to build and less expensive to buy parts for option, but will go with whatever the group prefers.

spritzer or others, I cannot find a working link to the bias circuit. I have been unable to find an SRD-7 pro so wanted to buy a regular SRD-7 and convert it to pro. Can anyone PM me the circuit or help me find a link? Thanks, Blueman2

I would love to have a PSU board as part of the GB. I was hoping Kevin Gilmore might be able to turn JimL's PSU design into a board, but I do not think he can get to that very soon. In any case, I am in for a PSU board as well, whatever the group decides. As for the Amp board, I am in even if it's cost is above $25. Probably anything up to $35 each if that is what it takes.

Were you able to send them the files for a quote yet? Excited about getting parts together for the project.

Good Idea. Worth the extra cost.

Yeah, I am pretty sure we are all Plan B or C from our spouse's point of view. So I am in for 2 boards. Let me know how much and where to send the paypal. Thanks! JimL, what wattage rating to you have for the resistors? Are they all the same? Also, for the .22uf 1000V caps, are those Axial or the rectangular type? Or does that matter? I have ordered a subscription to AudioXpress, but it takes 24 hours before I can have access to electronic copies. Can't wait to read your article!

mwl168 and MLA, sounds like both of you have had experience doing this. Would one of you be willing to lead a group buy? Alternatively, if one of you could set up the order on PCBNET on my account, I will be happy to make the buy and send out boards. I just do not feel comfortable knowing all the options to correctly set when ordering boards. Let me know. Sounds like enough interest that 10 or even 20 might be justified. Again, I will willing to front the costs and do the re-shipping to everyone if that helps. Otherwise, count me in for 2 srx6 boards! ooo! That is my next to-do. Though I figured the power supply would be simple enough for point to point. But if there is a board, I would definitely want to go that route. I recommend we not wait on it and go ahead and order the srx6 boards, and them come back later and do another group buy for the PS boards.

Thanks Kevin and mwl168. I am certainly in for 1 or 2 boards should anyone want to order a batch. I used pcbway.com to get a quote for 10, and it was about $130 shipped. So I am certainly happy paying $20-$25 per board from someone who takes the effort to order a batch of them.

MLA, thanks for the fast and helpful reply. I am pretty new to all of this (retired mechanical engineer who always wished he had gone EE). Yes, I prefer the SRX plus version but was scared off by the concept of getting boards made since I have no experience with that. If you were to be so kind as to do a board run, I would be in for 2! Let me know and I can paypal you money up front to help get this started. I just looked at subscribing to Audio Express, but did not see any way to gain access to past issues. Is there another way to buy the articles? Or are past articles available to anyone who is a current subscriber? I was going to buy both electronic and paper sub. thanks again!

This thread is a follow on to the original SRX Revisited thread and the SRX-Plus Group Buy thread. As of 2024, I count at least 12 members with working SRX-Plus Amplifiers: JimL congo5 MLA Sorrodje mwl168 luca jose blueman2 Juggernaut1101 tomislavkufrin simmconn oldie ============================================================= Here is an initial Bill of Materials for the Amp. Please provide input on errors and omissions and I will update. This is my first ever electronics build, so bear with me as I learn the ropes. I am initially building a KGBH psu, so do not have the BOM for the JimL shunt psu. I have linked to a post for the PSU BOM below. SRX-Plus Amp by JimL (SRX6 board by KG) Caps 7 0.1 µf/450 V 2 100 µf/6 V, NON-POLAR!! 4 .22uf / 1000v Resistors 18 100 O, 0.25 W gate stoppers for DN2540, and sense resistors 2 102 O, 0.25 W (source resistor for output cathode sink) ***Congo5 advises using 75 O instead 4 250 O, 0.25 W (source resistor for output current load) ***Congo5 advises using 200 O instead 4 500 O. 0.5 W 6 1.0 kO, 0.25 W gate stopper for 10M90S 2 1.43 kO, 0.25 W (source resistor for input current sink) ***Congo5 advises using 1.2 kO instead 4 2.0 kO, 0.5 W 4 5.1 kO, 1 W/500 V 8 124 kO, 0.5 W, 350 V rated 8 220 kO, 2 W, 500 V rated 4 300 kO, 0.5 W, 350 V rated 4 500 kO, 0.5 W, 350 V rated Silicon 10 Supertex DN2540 N-Channel depletion mode MOSFET (TO220) 6 IXYS IXCP10M90S current source (TO220) Trim Pots 2 20 O multiturn trimmer for output current sink—set current to 17 mA 4 100 O multiturn trimmer for output current load—set current to 7 mA 2 500 O multiturn trimmer for input stage current sink—set current to 1.33 mA 2 5 kO, 0.75 W multi-turn trimmer for input stage balance Tubes 4 12AT7, may also use 12AX7 or 5751 for top tube only 2 6SN7GTA or 6SN7GTB Connectors 3 3 pin 3 2 pin 1 4 pin Heatsinks 2 25 x 16.5 x 16.1mm Aluminum Heat Sink 4 42 x 35 x 25mm Aluminum Heat Sink This list is based on the BOM from the December AudioXpress article by JimL. I have adjusted it for the SRX6 board designed by Kevin Gilmore. Changes I noticed were: Use of a bipolar 100uf capacitor across the 5K input pot, which removed the need for 2 100uf caps and 1 100K resistor per channel. Change from 510K to 500K resistors going into the output tubes (6SN7's) Change from 250K to 300K resistors at upper input stage As noted above, changed values of the resistors in series with the trim pot of all the cascoded CCS as advised by Congo5 and MLA (Output current source: 200R in place of 250R, Output current sink: 75R in place of 102R, Input current sink: 1.2K in place of 1.43K) I recommend against trying to build the Shunt PSU as I am not sure JimL ever got this working to his satisfaction. I recommend you try another PSU. For the Shunt PSU BOM, refer to this post by jose. Note that the original board showed use of a TIL731 which is incorrect. It should use SPX431.