[Xcalibur255]

I see. I have a 6B4G push-pull amp and an EL84 push-pull amp, both using 6DJ8 as input tubes. Although they sound different they both sound great. I could not put one before the other. The first one gives about 7,5w and the other one about 12w. Same designer of both of them.

(Both are loudspeaker amps).

The EL84 kind of has a reputation for being sweeter toned than most pentodes or tetrodes. A well designed EL84 amp can certainly sound as nice as an SET like your 6B4G. Both of your amps provide a great cross section of tube sound between the EL84 and 2A3 "flavors" so it sounds like you have a very nice setup.

 

[bcowen]

1) Correct.
2) 100ohm 1/2W will work well, type doesn't matter as none of this is in in the signal path, all part of the heater supply.
3) Totally unnecessary. If you daisy chain them or run two sets of wire from the PCB, in both cases they are in parallel. I would daisy chain them.
4) Small m is milliohm, not mega they are 130milliohm resistors. Yes it will depend on how your heaters measure, I showed the calculation somewhere on the DarkVoice thread, let me see if I can find it...

Thanks! And especially on #4. I'm guessing the 130 Megohm resistors I was looking for wouldn't have worked too well. And also explains why I was having trouble finding them in a 5 watt rating. LOL!

 

[bcowen]

Exactly! It’s the kind of tube that tends to end up inside an enclosure.

Then no one can see that you’re rocking NOS Mullards or Tungsrams!

I had a 30 wpc integrated at one point using EL-84's. And you're right...they were all enclosed in a standard black box chassis. I do remember that amp sounding really good, and wish I'd never sold it.

 

[bcowen]

1) Correct.
2) 100ohm 1/2W will work well, type doesn't matter as none of this is in in the signal path, all part of the heater supply.
3) Totally unnecessary. If you daisy chain them or run two sets of wire from the PCB, in both cases they are in parallel. I would daisy chain them.
4) Small m is milliohm, not mega they are 130milliohm resistors. Yes it will depend on how your heaters measure, I showed the calculation somewhere on the DarkVoice thread, let me see if I can find it...

Found your previous post in the DV thread. I'm measuring 6.95v under load (with a test socket and tube in place) with 120.1v line voltage (which is pretty average normal for here). So if my calcs are correct I'd need a pair of 105milliOhm resistors, and they'd be dissipating 2.015 watts. Do I get a gold star, or did I goof even this up?


@L0rdGwyn 's notes from DV thread:

 

[L0rdGwyn]

Okay, so I lied about being done for the day, I put the new caps in, two TDK 33uF 250V polypropylene film caps. I did have to removed the PCB, and it was STILL a huge PITA. There is absolutely no slack from the transformer leads to the PCB, so getting them resoldered underneath was a true joy.



These are really pushing the limits in terms of what can be squeezed in here capacitance-wize. I had hoped to put in three per channel, but it just wasn't happening. So that gets you from 30uF stock to 66uF. -3dB point with 300ohm headphones stock was 17Hz. This will get you a -3dB point of 20Hz with 120ohm headphones, so drastically increases headphone flexibility. Really using anything below 120ohm is questionable anyway since the damping factor might make the bass pretty flubby.

It sounds great, I really like it. Really only a couple more things to do, mainly the new pot and power switch, but a couple things to experiment with as well (humdinger, higher-quality film cap on gyrator load). Probably another week or two.

 

[L0rdGwyn]

I will get back to you soon, @bcowen !

 

[L0rdGwyn]

Found your previous post in the DV thread. I'm measuring 6.95v under load (with a test socket and tube in place) with 120.1v line voltage (which is pretty average normal for here). So if my calcs are correct I'd need a pair of 105milliOhm resistors, and they'd be dissipating 2.015 watts. Do I get a gold star, or did I goof even this up?


@L0rdGwyn 's notes from DV thread:

You got it, 105mOhms per leg, you likely won't find a 105mOhm resistor so just go with 100mOhm. Power dissipated is 2W total for both resistors, 1W per resistor. So go with a pair of 100mOhm 5W wirewounds, could even get away with smaller 3W but they will get a wee bit hot.

 

[bcowen]

You got it, 105mOhms per leg, you likely won't find a 105mOhm resistor so just go with 100mOhm. Power dissipated is 2W total for both resistors, 1W per resistor. So go with a pair of 100mOhm 5W wirewounds, could even get away with smaller 3W but they will get a wee bit hot.

Perfect. Thanks!

 

[L0rdGwyn]

Finds from record shopping today. Both European reissues from the 80s but happy to have them, to the ultrasonic cleaner they go.



Replaced the woofer on one of my Snell Js, it was dented in with a vacuum cleaner handle LOL a true tragedy but we made it right. Handle to replace one of the inductors on the crossover as well, but managed to do it without removing the crossover from the cabinet, so relatively painless. They will be wearing their grills for the foreseeable future.

 

[bcowen]

Finds from record shopping today. Both European reissues from the 80s but happy to have them, to the ultrasonic cleaner they go.



Replaced the woofer on one of my Snell Js, it was dented in with a vacuum cleaner handle LOL a true tragedy but we made it right. Handle to replace one of the inductors on the crossover as well, but managed to do it without removing the crossover from the cabinet, so relatively painless. They will be wearing their grills for the foreseeable future.

Nice! I haven't been record shopping in a long, long time. Back in the mid-to-late '90's it was a normal Saturday ritual to hit the used record/book stores as people were dumping their LP collections en masse for "perfect sound forever."* * Wasn't unusual to come home with 50 LP's with a total spend of $100. Not as easy to find used LP's that are in good condition these days, at least where I live.

** (note: not slagging digital as I enjoy it a lot. Now. But a lot of improvements have happened in the last 20 years to make it so)

I was just listening to this one today. 2 LP set of a live performance that is superbly recorded, and with the exception of Telegraph Road (where the studio version has better pyrotechnics at the end) I prefer the renditions of every song on this to any of the studio versions. I bought it when it first came out and honestly don't remember what I paid for it, but probably $20 or less. Cracked up when I looked online and saw a couple for sale at close to $300.

 

[L0rdGwyn]

I was about to order some parts from Mouser for various projects, including a trimmer to make a humdinger for the DarkVoice heater supply, then thought I should clip in some parts and elevate the heaters before I even bother.

So I did that, elevated the heaters ~55VDC above ground by connecting the virtual center tap to a 220K+100K voltage divider from the B+ supply. The smoothing cap isn't necessary with the regulated supply but I threw it on there for good measure on the first go-around.



Hum is now completely gone, goodbye! Tested on various tubes that were previously noisy. So this is the way, virtual center tap + elevated supply, no point in bothering with the humdinger, DarkVoice is now humphrey.

 

[L0rdGwyn]

I made the elevated heater change permanent. I paralleled a second 2K resistor on the power LED PCB to account for the balanced heater supply. The power LED ground has to be disconnected from the ground bus and brought to the heater center tap so the LED does not see the 50VDC offset of the heater supply. The LED now lights up again.



Very happy the hum is gone with my black plate Fivre 6SN7GT, nice and quiet. All that is left to do is swap the pot and the power switch and consider A-Bing a higher quality film cap on the gyrator.

 

[Tjj226 Angel]

Make your own OTL now and compare : )

 

[L0rdGwyn]

Yes, I think I will, don't know when, maybe an improved version of this circuit without the space limitations. The sound is very good, surprisingly good really.

I am going to try running some 6N7 drivers in my 45 amplifier, I would like more gain on the input, I just purchased this quad of RCA 6N7G for that reason.



If it works out, and I think it will, that would leave me with a large pile of 6J5/6C5 without an amplifier, in addition to a pile of 6AS7G/5998/7802 without an amplifier. They would work very nicely together in an OTL.

 

[Xcalibur255]

Isn't 6SN7/6J5 usually considered to have enough gain to drive a 45? Since you didn't include your usual technical digression I'm all the more curious about your reasons for the change.