Millett "Starving Student" hybrid amp - Page 104

hmmm mine is all 26 or smaller. I'm gonna go ahead and use it. If I feel wires getting hot, I'll run 2nd strands

It's worth it...on my end. Nate, I appreciate your work on this. Personally, I had no idea these were getting so difficult to get! I'm in for a pair, and I don't care about the price!

Thanks man, seems that most folks are in your camp. There's only 1 pair of tubes left at this point.

Glad to hear that. I have 4 in my personal collection, but if nobody else wants the remaining 2 I'll take them. Gotta support the ones that contribute and I'd put you in the contributing category.

Nice! ...my comment about the price seems to go against the whole starving sub-thread, but I'd like to swap tubes for fun, and I already have a pair of Delcos.

Nate, it's good to hear that you could move the tubes. For what it's worth, I've had great success with this vendor:

2-TUBES,RADIO,AUDIO,HAM,CB [NOS] 19J6 - eBay (item 360106558695 end time Dec-11-08 13:37:41 PST)

I bet he has a few pairs squirreled away and he also offers sockets for $2 each.

That's good to hear, I just bought up the stock of tubes he was offering on eBay.

How does this BOM look:

I plan on using a similar BOM. Question though... What does item 21 (Tube LED) do? Provide a cool lighting effect for the tubes or something?

I would assume that 21 does in fact provide a cool lite under the tube.

Output cap voltage - 35V is too low, go with 50V minimum but recommended at least 63V. Muse FG in PSU performs worse than Nichicon HE.

I would bring up C6 to ~800uf to avoid hiccups.

Hope you enjoy your SSMH!

I thought with a low-power PSU like the 350mA stock Cisco, having big caps is the reason for the "hiccups".

I think it's a balancing act, to small a cap and the power supply sees the heaters as the load and can't keep up the cold start current demand, too big a cap and the inrush current to charge the cap exceeds the power supplies abilities. I've got a 680uF cap in my amp at work and definitely still get a little hiccup at the start. I may try backing that down to 470uF to see if that cures it, which is what has been reported to work by lots of other builders.

Why's this? The output caps only see 19V.

Reason I ask is I got a good deal on some 470uf 25V Nichicon Muse FS caps which I was planning on trying on the outputs.

Also I had a few other questions. How do you properly calculate output cap size vs frequency dropoff? I am using HD 580s so that will be a 300ohm load.

Also what do I need to consider when choosing bypass film caps? Do I even need them? I have Wima MKP10 .33uF and Audyn-CAP MKP .47uF on hand

Under normal conditions yes. However, if the tube or wiring fail, or there's a bit of discontinuity in the tube socket for whatever reason, the cap will see the full supply voltage. It's just good design practice. You can use the 35V cap, but it's not a good idea - always design for fault conditions.

-3dB point will be ~= 1/(2πRC)