Tube Rolling

[TurbOSquiD77]

Got around to measuring with the 6080. All are exactly or close to the same readings except OB on the high current boards. Is this due to the 5998 having higher plate resistance, and more than twice the moo's? I read that this won't affect heat, and that what does affect heat is the current the tube is pulling from the transformer. Apparently the 6080/6AS7G and 5998 are close according to a source found on head fi.

5998:
Class A Amplifier
Plate Voltage ................................. 110 V
Grid No. 1 Voltage Derived from
Cathode Bias Resistor ....................... 105 Ω
Amplification Factor .......................... 5.4
Plate Resistance (approx) ..................... 350 Ω
Transconductance .............................. 15.5K μ
Plate Current ................................. 100 mA
 
6AS7G:
Class A Amplifier
Plate Voltage ................................. 135 V
Grid No. 1 Voltage Derived from
Cathode Bias Resistor ....................... 250 Ω
Amplification Factor .......................... 2
Plate Resistance (approx) ..................... 280 Ω
Transconductance .............................. 7000 μ
Plate Current ................................. 125 mA


Let's measure with the 6080 vs the 5998 measurements in my post just before this one:

6080/12bh7a - 124 ohm at r1 on low current board - 12.1 ohm at R1 on high current - 300R psu resistors
Terminal Voltage (DC)
Low Current C4S
IA 150V   149.2V
OA 60-90V  62.9V
KregA 3-6V   5.26V
bRegA 150V   149.2V
IB 150V  148.7V
OB 60-90V   64.8V
KregB 3-6V  5.58V
bRegB 150V  148.7V

High Current C4S ( / indicates left and right High Current board measurements)
IA 190V 189.1/189V
OA 150V  148.7/149.2V
bA 0V  .3/.5mV
IB 0V   .3/.5mV
                   OB 90-110V  87.3/87V
bB 150V   148.7/149.2V



Is this okay or should I look into bringing high current OB's voltage back up when running the 5998? However, OB on the low current board is fine. Interesting! I see pcb traces going through R2B, R1B, Y/Y+, and in the opposite direction being output caps/headphone jack/OB low current board, as well as pin 6 and 3 on the 5998 socket.

Possibilities:
R2B (22KΩ 5W)
R1B (31.6Ω ⅛W)
Y/Y+ (33KΩ ⅛W)

Nice post btw - just for everyones reference:
http://bottlehead.com/smf/index.php?topic=4965.0

Quote from: TurbOSquiD77 on February 14, 2017, 03:42:42 pm
Helps a ton! How might I apply this to the power circuit?

That's quite a can of worms.  You really should leave this alone.  Trying to alter the operating current of the output stage can have adverse effects on the operation of the amplifier, and the presence of the shunt regulator means that the whole amp would need to be redesigned if this is messed with.  Additionally, there are very few dual triodes with enough transconductance to offer the low output impedance available with the 6080.

Not about to go that route if it involves much more than component value changes. That is, if changing R2B..etc is where this is heading. Just hoping to work towards keeping her healthy

Huzzuh!!!!

[Paul Birkeland]

When OA and OB on the small C4S board are a little low in their range (like yours) that will bring the OA and OB voltages of the high current C4S boards that feed the 6080 down a little bit as well.

To nudge them back up, the R1 on the center small C4S board will have to be lowered a bit.  If you're at 124R now, try a 113R and see if that perks up your plate voltages (and consequently 6080 cathode voltages) a little bit.

[TurbOSquiD77]

Cool, I will try and dial her in. Thanks Paul

Will having the cathode voltage low at OB on the high current boards be a problem if I continue to use the 5998?

[Paul Birkeland]

Nah, better a little low than really high, though there's some thermal headroom on those heatsinks.

[TurbOSquiD77]

Numbers are looking good after the adjustments - will share soon!

Quick question before hitting the hay....

I've replaced the stock 270R 5W power resistors with 300R 5W. Easy, kind of!
I am now (after some patience and time and in the end rebuilding the entire power supply with new parts anyways [UF4007-GP-TP Ultra Fast rectifiers - found em! ]) running 300R 10W.
Holy hell that's a tight fit - they are pretty long.
All voltages checked out great - same or better numbers than those previously posted.

I think I'm hearing some clipping. Very light, seems intermittent, and at odd times on the same track. But sometimes at the exact same time, on the same track. It's just a little snap/pop right? But, the C2A should be more than enough for Beyers and Senns. hmmm

Happy listening, pics to come.

-T

[TurbOSquiD77]

Seems as if my soldering iron (not me of course) caused some damage to the Nichicons - metal is showing a bit. I have new ones on the way. Power transformer is making more noise than usual. However, all voltages check out great.

Can I redo the incoming voltage test with everything connected? Since I've modified the power resistors with 300R 10W's. I also had to curve the rectifiers in the power supply quite a bit to get them around the resistors. This might be contributing to something but not sure.

I've also been battling dirty power coming from my PC. What a nightmare. Many steps have been taken, and next is a power conditioner.

[Paul Birkeland]

Yeah, this is part of the process of doing strange modifications.  There may be problems that come up that will take some time and effort to resolve on your own (I haven't tried the mods, so I'm not sure what might be happening).

Your incoming line voltage is very, very unlikely to change appreciably.  If you live in an area where this happens, you will already be very aware!

What happened to the UF4007's that came with the kit?  Was there an issue that required their removal?  From where did you source the new diodes?

The power transformer shouldn't be making any additional noise unless you've put a considerable additional load on it.  This would generally be reflected by low voltage measurements and hot parts.  Just as a test, you can pull all the tubes out and turn the kit on, then listen for the noise again.

[TurbOSquiD77]

Yeah, this is part of the process of doing strange modifications.  There may be problems that come up that will take some time and effort to resolve on your own (I haven't tried the mods, so I'm not sure what might be happening).

Your incoming line voltage is very, very unlikely to change appreciably.  If you live in an area where this happens, you will already be very aware!

Totally understand! I think I've created my own confusion....
Long story short I believe my new dac is the source of a very small pop/clipping sound which is randomly present in my music. New dac in conjunction with installing 10W power resistors (and second guessing my fitment/soldering, damn things are long!) made me think that the C2A power supply was the source of the issue.

What happened to the UF4007's that came with the kit?  Was there an issue that required their removal?  From where did you source the new diodes?

I rebuilt the entire power supply by properly desoldering, removing, cleaning with Caig Deoxit D5/D100, re positioning brand new parts along with the 10W 300R, soldering with Cardas silver solder (with lead), and cleaning with Deoxit D5/D100 and a pick to scrape the flux, topping it off with Deoxit Shield. Cleaned the transformer leads as well in the same manner. Everything looks super good! 

Sourced all parts from Mouser, the exact values of the stock kit.
294-270K-RC
http://www.mouser.com/Search/ProductDetail.aspx?R=294-270K-RCvirtualkey21980000virtualkey294-270K-RC

UF4007GP-TP
http://www.mouser.com/Search/ProductDetail.aspx?R=UF4007GP-TPvirtualkey54720000virtualkey833-UF4007GP-TP

The power transformer shouldn't be making any additional noise unless you've put a considerable additional load on it.  This would generally be reflected by low voltage measurements and hot parts.  Just as a test, you can pull all the tubes out and turn the kit on, then listen for the noise again.

It seems as if the power transformer and I have a love/hate relationship. Every time I change something, rebuild, or upgrade I find myself with the notion that the transformer is louder and/or hotter than before. Maybe it's because I'm worried. Maybe it's because I goofed (yep once lol). But I remember that when I did goof, the transformer was much more crunchy pissed cyborg sounding and HOT than it is now. Transformer hum is always audible, but only when I put my ear 6-12" away. It's a little bit higher pitched of a hum, not low and smooth. It does get hot... typically I can grab the transformer for 5 seconds or longer before needing to let go. That is, when she's been on for a couple hours pumpin' jams. I never see smoke, but do see heat dissipating which can be mistaken for smoke depending on lighting.

Those 10W resistors are huge! Can I connect the diodes to the same terminals, but in a different fashion? Such as, upper vs. lower terminal. This would help positioning them immensely, and also allow me to straighten the diodes. As of now, a couple of the diodes are curved to fit around the resistors, as the resistor leads won't allow me to move any further away from the diodes. Or, I can just use 5W resistors if 10W isn't absolutely needed, and without consequence.


Thanks Paul,
I'll try to keep the questions to whether or not I can do something, or what parts to use, rather than spewing my issue before taking all the troubleshooting steps. I have come to the conclusion my issue is not the C2A, it is my Amanero USB in the dac that is causing a random pop noise. C2A sounds good right now

-T

[Paul Birkeland]

The 10W power supply resistors aren't necessary, just use the 5W ones.

Deoxit is a cleaner for connectors. I would recommend against using it while soldering. The solder Flux exists to clean and prep the joint for you, and if Deoxit leaves behind any corrosion inhibitors, it may actually make soldering more difficult.

[TurbOSquiD77]

Mental note made. May only use Deoxit for post solder joint cleaning - it does work very well to remove flux residue. I did not realize the solder flux cleaned the joint so well before hardening. Thought it was just a little thing*

Popping issue fixed by using ASIO Bridge software. Sounding good now

Will the diodes be okay being curved a bit? From a physics perspective I'm not quite sure.

[troplin]

Mental note made. May only use Deoxit for post solder joint cleaning - it does work very well to remove flux residue.

AFAIK, those active contact cleaners should also be washed away with a normal solvent, because the the residues can cause corrosion themselves!
I don't know deoxit specifically, but I know that from the "Kontakt" brand that is popular here, that there are 3 types of spray that are best used together:
- "Kontakt 60" for deoxidation
- "Kontakt WL" for general cleaning
- "Kontakt 61" for protection against oxidation
From what you read online it's a common mistake that deoxidizer is used without washing it away.

[TurbOSquiD77]

Thanks troplin! I picked up some CRC contact cleaner (quick dissolve kind) and have been using it with a foam swab so I don't over spray.

Update on resistor value changes for 12BH7A and E80CC:

5998/12bh7a
113 ohm at r1 on low current board - 12.1 ohm at R1 on high current board
300R 10W psu resistors
Jupiter Copper Foil .10uF 600V on low current board
Rebuilt power supply with standoffs to accomodate 10W power resistors

Terminal Voltage (DC)
Low Current C4S
IA 150V   149.3V
OA 60-90V  70.5V      +7 from previous 124 ohm R1
KregA 3-6V   5.56V
bRegA 150V   149.2V
IB 150V  148.7V
OB 60-90V   72V     +7 from previous 124 ohm R1
KregB 3-6V  5.51V
bRegB 150V  148.7V

High Current C4S ( / indicates left and right High Current board measurements)
IA 190V 190.5/190.6V
OA 150V  148.7/149.2V
bA 0V  .3/.5mV
IB 0V   .3/.5mV
OB 90-110V   81/79.2V      +6 from previous 124 ohm R1
bB 150V    148.7/149.2V



5998/ e80cc
453 ohm at r1 on low current board - 12.1 ohm at R1 on high current
300R 10W psu resistors
Jupiter .10uF 600V on low current board
Rebuild power supply with standoffs

Terminal Voltage (DC)
Low Current C4S
IA 150V   149.3V
     OA 60-90V  68.4V
KregA 3-6V   4.24V
bRegA 150V   149.3V
IB 150V  148.7V
     OB 60-90V   64.9V
KregB 3-6V  4.58V
bRegB 150V  148.7V

High Current C4S ( / indicates left and right High Current board measurements)
IA 190V 189.7/189.6V
OA 150V  148.7/149.3V
bA 0V  .3/.6mV
IB 0V   .3/.5mV
        OB 90-110V 74.8/76.8V
bB 150V   148.7/149.3V



Moving from 470 ohms to 453 ohms at R1 yielded a value of 1V greater at OA, OB on low current board, and .5 ohms (left) 0 ohms (right) at OB on the high current boards. So, 17 ohms less yielded 1V greater or less. I have 412, 422, and 432 ohm values available to try. 412 ohms maybe?

Are there any reasons why I should not go to a lower value with R1 on the low current board? I want to make sure this position isn't relied upon other than voltage levels, or if voltage is the only thing I'm concerned with here. I could possibly go lower for the 12BH7A as well - less than 100 ohms?

Regards,

-T

Ps. She's sounding really, really good  and the power transformer makes next to no noise for the first couple hours, but starts to make a bit of noise after that - it does get quite hot to the touch but not enough to burn me.

[Paul Birkeland]

None of those voltages look particularly concerning.  What you have to look out for is having something like 50V or 100V coming out of the small center PC board, or having unusually low Kreg voltages in the regulator. 

[L0rdGwyn]

Anyone rolled the 6AQ5's to any effect?  I picked up a 5-tube sleeve of Sylvania Gold Brand 6005's to try when my build is complete.

[Paul Birkeland]

The 6AQ5s don't have a ton of influence over the sound, but let us know what you find.

-PB