grounded grid

[joehpj]

one stupid question: Is this fixed bias or self biased?

[kevin gilmore]

2sc5171 not recommended for new designs, which means soon to be discontinued. different pinout than the layout, it could make another layout if people are interested. Or you mount it upside down which is possible.

500 piece minimum from digikey, non-stocked at mouser.

adjustable bias, current sources at the top

Edited December 31, 2015 by kevin gilmore

[congo5]

Its running, using KGST PS @ + / - 350v

all trim pots responsive.

Bias set at 80%   .8V across 50R for now

Output with 100x probe = input at 1x

Mouser slow this week so using MJF15030 (backwards) for the KSC2690A's

Balance adjusts to 0V

Offset adjusts -132v to -146v  so need to track that down... may change when using + / - 400v and 2690A

led's lit, no smoke, stable voltages

Edited January 8, 2016 by congo5

[spritzer]

Change the tail resistor for the offset pot and it should work.   

[congo5]

I'm waiting on the postman to deliver some Rexolite 2200 2oz copper .125 thick boards, today.

 Not sure if I should use this one anyway its 1oz copper.

The tail resistor would be the 120R connected to the pot wiper, right?

[kevin gilmore]

About 300 ohms is the right number, don't know if that's total or just the tail resistor. Less ohms in the pot and most in the resistor is what we are aiming for.

zener needs to change to 18v

Edited January 2, 2016 by kevin gilmore

[JoaMat]

Replaced 2sj79/2sk216 with ksa1220/ksc2690 on one Blue Hawaii and one DIY T2. No negative surprises so far.

[JimL]

Sounds like this is the new improved Blue Hawaii?

[kevin gilmore]

nope, that is a different board. with the fets replaced with bipolar.

practically they are almost identical.

[joehpj]

How about those VR for balance and offset?

I think mounting on the same side of tube will make it easier to adjust when operating.

edit: and LEDs?

[kevin gilmore]

all those parts can be mounted on the other side. latest version of the board has silkscreens both sides for the pots

[joehpj]

One more question.

How about paralleling 6S4 to get 20ma@400V ? Comparing to EL34s, those are real triodes and have a much more reasonable price for NOS.

Any pros and cons?

[nopants]

Aren't Winged-Cs like 20-30 a pop? They're not really the bank-breaking part of the build

[mwl168]

28 minutes ago, nopants said:

Aren't Winged-Cs like 20-30 a pop? They're not really the bank-breaking part of the build

Winged C EL34 from reliable vendors like Upscale Audio is around $70 US each. 

Edited January 9, 2016 by mwl168

[joehpj]

Actually, I could get 6S4 NOS for about $10 each.(out of production so of course NOS) Dirt cheap for getting octets.

Winged Cs or sth like re-issue Mullards are really not bank breaking. But for NOS vintages like Mullards or RFTs......... 

Of course EL34s looked much better when lit up.

[kevin gilmore]

2 hours ago, joehpj said:

One more question.

How about paralleling 6S4 to get 20ma@400V ? Comparing to EL34s, those are real triodes and have a much more reasonable price for NOS.

Any pros and cons?

yes you can do this, you need adjustable cathode tail resistors.  basically the same as srm007t2

board is going to get a bunch bigger

[spritzer]

It can be done but I don't see the point.  Seriously, go look up the EL34 curves when it is triode strapped. 

[wink]

I guess the point here is that an octet of NOS 6S4A's is still a lot cheaper than a quad of NOS EL34's.

Once you pay for the larger board size and double the amount of tube bases and extra parts, you're ahead.

Still, seems an exercise in futility to me if you're striving for "moar bettah".

 

[mwl168]

6 hours ago, joehpj said:

Actually, I could get 6S4 NOS for about $10 each.(out of production so of course NOS) Dirt cheap for getting octets.

Winged Cs or sth like re-issue Mullards are really not bank breaking. But for NOS vintages like Mullards or RFTs......... 

Of course EL34s looked much better when lit up.

I just spent the past few weeks researching EL34 options. Winged C EL34 price from reliable sources are actually pretty close to that of the RFT/Siemens EL34. Matched quad of NOS Mullard EL34 are on a complete different price bracket.

Can you share where you find 6S4 for $10? Last time I look, a matched quad would set me back about $90 US. 

Edited January 10, 2016 by mwl168

[spritzer]

You can find unmatched 6S4A's for around 10$ each, maybe less.  Having bought a few hundred of these over the years I've had to throw out 20% (and they were sold to me as tested) and it's not easy to properly match a quad...let alone an octet. 

As for the EL34's, the JJ's are excellent for the price and the new production Mullard's aren't bad at all. 

[mwl168]

Yes, that makes total sense. The shop I inquired about the matched 6S4 told me they'll have to weed out many tubes to find a matched quad thus the high asking price.

The JJ EL34 is an interesting case, most of the stuff I read on the web either praise their sound or condemn their reliability. Unfortunately I did not pay enough attention to plot the data points and see if there is a correlation with time/period of production.

I've read good things about the re-issue Gold Lion KT77. Anyone has experience with them?

[joehpj]

13 hours ago, mwl168 said:

Can you share where you find 6S4 for $10? Last time I look, a matched quad would set me back about $90 US. 

My 6S4s are from a local dealer outside of US and not selling worldwide. Sorry for that.

He claimed all tubes are matched on TV7 for free.

However, I rarely believed in those commercially matching services. Tubes need about 50 hours or even more to become really stable as I know. If the QC processes are total 10 hours in the factory. Then we'll still need many hours to lit them up and wait. Most of those tube shops only put tubes on a tester for 1 hour or so. Not even mention those tubes are not matched on your amp's working point. So I've already gave up getting real matched tubes.

For new-production EL34s, I recently found a dealer on Taobao claiming they age the tubes for hours until they stabilize and traces the curves individually. Then matching is based on those curves. If they really did those processes, and this will be the best matching service I've ever know. If someone is interested too, then I'll post the link.

Any opinion on matching tubes?

After searching, I think EL34s are more fun to play with. Much more choices and yes, better. So I think I'll go for EL34. Feel sorry for my wallet.

Really interested in Gold Lion KT77s too. What's sonic difference between el34, 6ca7, kt77?

Edited January 10, 2016 by joehpj

[mwl168]

Thanks joehpj for your response. I did a little bit of search after reading your previous post and found unmatched 6S4 for less than $5 US each at a couple US vendors. 

I share your view points of tube matching and for that reason have always been skeptical of the claims. I have bought tubes from Upscale Audio because I like their 72 hours burn in process for power tubes and I trust them. They do come at a higher price and I don't know if they'll match the desired tubes under specified operating points. 

For that matter, one has to wonder what happens to those tubes that are excluded from the QC and matching process especially dual-section tubes!

I've always fantacized about building a simple tube testing and matching circuit for my own purpose ( I use a lot of 6SN7 and 6AS7 in my gears) But I have not done the homework to learn how to do it right. 

[Laowei]

Wondering has a triode strapped 6V6GT been considered as a candidate in an electrostatic amp? They were spec'd for Veritcal Deflection Amplifer service in TVs.

In my experience, in a classic P-P Class A circuit, they can sound as good as a DHT 45.

The reissue Tungsol is inexpensive and on par with NOS. 

Edited January 10, 2016 by Laowei
Fucking iPhone

[spritzer]

Maximum DC voltage 315V, no way we could use it.