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Tubelab SE build and power supply questions.

Does it happen on both tubes? Some drift is normal as it is usually due to variations in the voltage coming out of your outlet. Is your A/C on and cycling? Put a meter on B+ and watch it...it will probably go up and down along with the bias current. Neither the B+ nor the bias rails are regulated on this amp. You just need to leave some margin in your bias setting to accommodate when your power outlet is up.

There will also be some drift as components heat up, so be sure and do a final tweak on the bias after it is good and warm. Also, some new DHTs seem to drift for a while at first. My Shuguang's did that for the first few hours of life, but they are pretty stable now.

I had one used eBay 45 that had a marginal heater connection. After the amp was on for a while the one channel would drift in and out a little due to the bias voltage floating around. I couldn't figure it out at first...I though it might be a bad FET. I later noticed that the cathode was getting a little dim when it would fade-out and I could wiggle the tube and it would come back. Wasn't the socket...just a flaky old tube.
 
General questions regarding component choices

1. C5 mod-The second most common modification is to add a supplemental power supply capacitor. Most users have added a motor RUN (not start) capacitor in parallel with C5. I read somewhere else that a 1uF paper in oil capacitor was also used. I also have 4 Solen PB-MKP-FC 50uF (400V) and was thinking of using 3 in parallel instead of the electrolytic (along with the 1uF paper in oil). What are the benefits of each and what would be the Best choice? I realize that the latter choice would involve lowering the PS B+ ( Unless I kept the electrolytic, and used all 4- in a 2X2 config.)

2. C9 and C11 couping caps- I have a bunch of 0.22uF Russian teflon's and was wondering if anyone else has tried these and compared them to the traditional boutique caps?

3. Insulators could be used on the CCS and mosfet heat sinks?

4. Some users may want to use their favorite brand of boutique capacitor here. There is a chart in the Applications page that will help you pick the value of C4. I could not find the chart under the link to help with C4 choices..

5. Resistor upgrades- Is it worth upgrading some of the resistors with premium parts such as tantelums for R18,29,33, and 34 and others? Non-Inductive WW's for the larger wattage resistors (not sure if this one is appropriate or not)?

6. Choke upgrade - What would be the difference in sound characteristics between the 6H triad or the 10H hammond choke?
 
1) The idea here is to use some low-ESR film cap to bypass the electrolytic. You can use whatever film cap you want...Solens are a fine choice. You can get the same performance from a motor run cap as suggested by George (they are typically film in oil). You can also substitute the electrolytic entirely as you are suggesting. In fact, someone on this board built a Simple SE with all film motor run caps.

3) Sure. As a precaution, you should probably ground the heatsinks somehow so that you know for sure they are not live.

4) Best thing to do is download PSUD II and run some simulations to tune the value of C4. I think the chart in question was lost in a hard drive crash.

6) I never "heard" any difference (I tried both), but it should reduce ripple and improve regulation. Note that a larger choke kind of needs more C5 to keep the supply damped. Again, this is something you can observe in PSUD simulations. I went with a 220uF part that fit perfectly on the PCB (Digikey P7457-ND).

I can't really speak to the boutique parts...not really my thing. I suspect #2 is a matter of taste and #5 is even more so.
 
russian teflon

i use russian teflon C9 and C11 couping caps and they sound great havent tested any other caps yet but my amp runs and sounds great i do use a triad chock that george used on his build x14 i think dont remember my amps on aluminum plate with black walnut casing 200ma panel meters with leds its pretty sweet
 
1)
4) Best thing to do is download PSUD II and run some simulations to tune the value of C4.

I found your PSUD file from a previous post and have been tinkering with it. I haven't figured out how to add components to the schematic myself yet, as the help file doesn't work on vista (imagine that, wtg MS). One question though, I always get the rectifier exceeded IFRM warning. How far can you go over on that parameter before it's a problem?

I noticed that Solen now makes HV film caps with values over 200uF now...it appears you could make an amp with all Solen's if you wanted to. How does the ESR on the motor run caps typically compare with the Solen's (.001ohm)?
 
Looks like I used a 100uF, 450V (Mouser 647-UPT2W101MHD) in both the C6 and C7 positions. C6 definitely needs to be 450V. I was concerned about the voltage on C7 at startup before the B+ rail came up and the FETs started drawing significant current (enough to invoke a voltage drop across R6). However, I imagine many other have used a 350V cap here and it has been fine.
 
Some transformers have a bias tap or additional filament windings. These are not used and must not be connected to anything. Some transformers have a shield or ground wire. It should be connected to the ground lug on the power connector. This is a thin grey wire on an Allied transformer.

George

I was just getting ready to start a post about this grey shield wire on my Hammond (Allied?) power transformer, part # 6K7VG. The grey wire is listed as part of the SEC3 on the PT (see photo) ... so I wasn't sure if I should attach it to the ground lug or not. I was unsure if the shield was only to be used with the SEC3 output. Is it actually the 'equipment' ground for the transformer? Thanks!
 

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I see your point.

Yes, the grey wire *is* the one you should ground, as per George's quote you noted.
It's the shield, not part of the actual secondary.

Should I also run a ground wire (with a ring terminal on one end) between one of the bolts holding the transformer in place and the main/star ground? Or is that redundant?

Note, my bench setup is all mounted to a piece of plywood.

Thanks