Valvecaster standard Shopping List at Small Bear

[lowend]

please excuse the thinking out loud

You only need the big resistor(s) for the 6111 version. To run the 6111 heater from 12 volts you need to reduce it to 6.3 volts. That's what the 19 ohm / 3 watt resistor does. I used two 10 ohm in series - they were 5% tolerance,  I measured them at 19 ohms - perfect!

something I got off another thread by freqCentral

That's twice the voltage suckage at the same current so twice the resistance required, checks out with my maths, so I'm inclined to trust my power calculation as well, just wonder if it is a safe margin, 1W of power handling for .81W dissipation?

[PRR]

3V to lose at 0.3A.... 2.7V/0.3A if you obsess about small-stuff.

At low current, the 12AU7/AX7s can run OK at 5.6V or 6.6V, so there's no reason to get fussy.

I'd call it 9 or 10 ohms at 1.0 or 0.9 Watts.

If you put 0.9 Watts in a "1 Watt" resistor, do not give a warranty longer than 30 days. It may run 90 days, maybe years, especially well-ventilated. OTOH I have seen 0.55W in a 1/2W part fail in 5 weeks.

So we save 30 cents on the part, but it takes an hour to open-up, find the solder, extract the corpse, find something else to put in there..... when you are your own warrranty tech, just over-size any hot part so you don't have to do it over again.

It is VERY reasonable to DOUBLE-SIZE any nickel/dime resistor working hot. In this case, I'd go 5W because they are not much more expensive than 2W parts. They are bigger but you WANT big to throw-off the heat. Some modern "2W" parts are teeny: they do carry 2W per spec but the surface temperature will burn skin or insulation. For hobbyist stuff, spread it around to a mellow "hot" instead of a "Yow! HOT!!".

In a 1/2W catalog: Four 39 ohm or five 47 ohm in parallel is reasonable.

In a 1/4W catalog you need nearly 10 pieces at 91 or 100 ohms. The cost is small but it's quite a mess to solder-up.

When using multiple resistors to throw heat, leave lots of space between. At least a body-width, several millimeters.

[lowend]

I'll have to see how I get on with a 5pack of the 1/4W ones since that's what I just ordered.  I did keep checking back to this thread to the end too!

Generously spaced and ventilated will be the order of the day thanks. If it keeps the valves working 10 years instead of 5 it will be worth it. It has to be better than 4.5V anyway.

I added tuning caps and some more hardware parts for standing the circuit board and mounting the valve internally.

2    0611     Jack, DC Power, 2.1 mm All-Plastic, Round(All-plastic Round)   $1.25    $2.50
2    0708    Socket, 9-Pin With Shield (9-Pin Socket w/ Shield)                     $2.20    $4.40
4    1005A    Alpha Single-Gang 16mm, Solder Terms, Linear & Audio Taper(100K Audio)
   $1.25    $5.00
2    1005A    Alpha Single-Gang 16mm, Solder Terms, Linear & Audio Taper (50K Linear)
   $1.25    $2.50
1    2303B    LED 8mm High-Brightness Clear, Colors(Orange)
   $0.80    $0.80
1    2303B    LED 8mm High-Brightness Clear, Colors
(Blue)
   $0.80    $0.80
4    0600A    Jack, 1/4 in. Mono Neutrik #NYS229 (Jack 1/4 in. Mono Neutrik NYS229)
   $1.15    $4.60
1    1405    Capacitor, Electrolytic, Radial 16 V 220 mf. - 470 mf.
(220 mf.)
   $0.45    $0.45
1    1405    Capacitor, Electrolytic, Radial 16 V 220 mf. - 470 mf.
(470 mf.)
   $0.45    $0.45
2    0902    1.1K to 6.2K - Individual
(4.7K)
   $0.15    $0.30
2    0904    43K to 220K - Individual
(100K)
   $0.15    $0.30
2    0904    43K to 220K - Individual
(220K)
   $0.15    $0.30
2    0905    240K to 1 Meg - Individual
(470K)
   $0.15    $0.30
2    0905    240K to 1 Meg - Individual
(1Meg)
   $0.15    $0.30
4    1101B    Capacitor, Panasonic ECQ-V .01 mf. - .1 mf.
(.047 mf.)
   $0.30    $1.20
2    1101B    Capacitor, Panasonic ECQ-V .01 mf. - .1 mf.
(.01 mf.)
   $0.30    $0.60
2    1107    Capacitor, CDE DME Series, 1 mf. 100 V
   $0.70    $1.40
1    6013    J-B Weld Kwik Epoxy
(J-B Weld Kwik Epoxy)
   $5.95    $5.95
8    8007    Threaded Stud, 4-40 x 3/8" High x .187" O.D.
(Threaded Stud 4-40 x 3/8" High x .187" O.D.)
   $0.35    $2.80
3    8010A    Mounting Bracket - Pack Of Four
   $1.20    $3.60
2    8003    Screw, Pan Head 4-40 - Bag of 10
(3/8")
   $0.85    $1.70
2    1201    Capacitor, Xicon, 630 V .001 mf. - .022 mf.
(.022 mf.)
   $0.30    $0.60
1    1202    Capacitor, Xicon, 630 V .033 mf. - .047 mf.
(.033 mf.)
   $0.40    $0.40
10    0900    1 Ohm to 100 ohms - Individual
(47 ohm)
   $0.15    $1.50
1    0223    Switch - DPDT Toggle Taiway 2MD1T1B1M2RE
(2MD1T1B1M2RE)
   $2.10    $2.10
1    8004    Screw, Flat Head 4-40 x 1/4 - Bag of 5
   $0.40    $0.40
1    8005    Nut, 4-40 - Bag of 5
   $0.40    $0.40
6    0807    Black Fluted Silver Center, Small
(Silver Center Small)
   $0.65    $3.90

Sub-Total    
$49.55 not bad for the best part of two pedals

[Govmnt_Lacky]

Sub-Total    
$49.55 not bad for the best part of two pedals

Good list however, you did not include the priciest parts. The Tubes, 3PDTs, enclosures. Those alone will probably be in the 40-50 dollar range.

[user]

He already has them.

[lowend]

Yes, I was expressing my happiness at spending so little more.

I estimate you could get away with about 30 buckeroo for those pricey items per pedal so around US$55 + shippings, vero if you want it, solder, wire.

The list includes 2pack epoxy which will last many many builds btw. I got 5 valves for $23 + shipping off ebay. DIY your box out of sheetmetal for pennies, build it on the valve and you're looking at a lot less than $55. All those nuts and bolts and doodads add up.

I could have bought one valvecaster complete, powdercoated, w/ anodised valve shield, for $180NZ which is about US$125. I'm less than that for two but mine will be not so flash. I'm happy.

[PRR]

> If it keeps the valves working 10 years

Ten years??

A lightly-worked 12AU7 with 6.0V-6.4V on the heater _should_ out-last us all.

The 12AU7 in my VTVM is from 1972 and has been powered-up 24/7 for almost half of four decades. A few years back I had to clean the pins and socket, decided to throw in another. It worked nearly the same, so I put the original back.

In theory the heater evaporates and breaks, like a light-bulb. But heaters run much cooler than lamps and last exponentially longer. If not abused (series-string start-up, 5-foot drops into dumpsters), a failed heater is almost never seen.

If the heater fails, it just had a flaw and was GOING to die young.

There's other ways tubes fail. POWER tubes work hard and tend to melt their grids or exhaust their cathodes. High-gain 12AX7 has too-close electrodes which are prone to touch. But the 12AU7 is about as fussy as a potato.

[lowend]

That's nice to know. I've got 6.sommat volts coming my way. Any sage words about the survival on 4.5V?

I plucked the ten year figure out of the air as I know they go at least a year but there seemed to be some serious doubt on the wisbom of underpowering the heaters. Maybe it was a big waste of time and resistors, maybe not.

Edit:  I already have a 9V supply. I could have got a 12V but here's some stuff I dragged off about page 6 or 7 of the valvecaster thread

Personal Message (Offline)
   
   Re: Tube boost + overdrive running off a 9 volt battery
« Reply #145 on: January 24, 2008, 10:18:00 AM »
   Reply with quote
"I don't think that lower heater voltage (like 9V for both heaters) would lower tube life. It would just sound different that it's supposed to."

Lower heater voltage is actually worse. From the Tone Lizard,

Look about halfway down the page of this link to see the chart:

http://www.tone-lizard.com/Marshall_Myths.htm


"I would like you to study the diagram below carefully. It is from the book Audio Cyclopedia, by Howard M. Tremaine. It deals with the prospect of running the filament voltage on any tube at other than 100% rated value. The illustration shows that tubes will fail prematurely if the filament voltage is either higher or lower. For maximum tube life, the voltage must be 'right'."

"From the chart above, you should be able to determine that if a tube has a usable life of approximately 6,000 hours with its filament operated at 100% of the rated voltage, the tube's life expectancy is reduced to 1,000 hours just by lowering the filament voltage by 10%. This translates to a 6.3VAC tube being run at approximately 5.67VAC, or the input voltage lowered from 120VAC to approximately 108VAC. Ask your local tube guru if they have read Audio Cyclopedia. However, even 'experts' can disagree on anything and everything. GE published data confirming tube life is decreased substantially by raising the filament voltage, although tube life can be increased by lowering the filament voltage very slightly. The performance of the tube was purported to be more 'even' over its useful life. However, it should be pointed out that the slightly lowered filament voltage GE 'recommends' proportioned to the plate voltage (via your VariacTM) won't make a difference to our ears. People who set their VariacTM to 100VAC are only asking to replace tubes every other month. The GE report also stated that the transconductance of the tube was reduced dramatically, and an audible deterioration in performance was noted when reduced filament voltages were employed. So why bother?"





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mojo_hand
Posts: 76


View Profile Personal Message (Offline)
   
   Re: Tube boost + overdrive running off a 9 volt battery
« Reply #146 on: January 24, 2008, 04:24:44 PM »
   Reply with quote
There are a lot of different figures on tube life and heater voltage, in part because different tubes respond differently.  Those with thoriated heaters, for example, do well when run at rated voltage for their first 200 hours, then dropped to 95% of full voltage until they approach end of life. http://www.cpii.com/docs/related/22/AB18.pdf  Dropping to 90% of rated voltage after the initial 200 hours may increase filament life to the point that heater failure will be eliminated as a cause of (thoriated) tube failure. http://www.burle.com/cgi-bin/byteserver.pl/pdf/tp202.pdf  Tubes with oxide-based heaters are different.  Power tubes can have their life shortened by running at lower heater voltages, but others often benefit from slightly lower voltages: at 10% above rated voltage, life will be cut by half, at 5%-10% below rated voltage, tube life will be significantly enhanced at the cost of slightly worse performance in various other regards. http://www.pmillett.com/Books/Tomer_1960_Getting_the_Most_Out_of_Vacuum_Tubes.pdf  I suspect that the author cited by the earlier poster was thinking of power tubes when he condemned running tubes at reduced heater voltages, since it is very true with those.

My recommendation would be to never run power tubes at anything but their rated voltage, and to rectify, filter, and regulate that voltage if you're using expensive tubes.  For other types of tubes, if high longevity matters more to you than squeezing every last bit of performance out of it, rectification and filtering are also good, but the target voltage should be 5%-10% below rated value.  Anything lower than 90% of rated value will cause worse performance without enhancing tube life, and may actually shorten life.  Using tube coolers and/or cooling fans will also increase life, often doubling it.

Using 9v in place of 12.6 for heaters is not a great idea from any perspective, in this schematic it has to be considered a matter of convenience rather than good design.

[PRR]

> tubes will fail prematurely if the filament voltage is either higher or lower.

Like most of Tremaine's publishing, this is out of context.

If a tube is asked to work HARD, a cool cathode will fail to deliver desired current and the power output will not meet specs. Has the tube really failed? If you fix the too-low voltage, it will be fine again, perhaps after some hours to simmer the thorium up from the oxide.

If the tube is not working hard, some underheating may be perfectly fine. The most common example is Dynaco preamp working 12AX7 with low plate current and 11V on the 12.6V heater.

But I would not go any lower than that (5.5V on 6.3V connection). Especially if you have no reason to go lower. And you don't. You picked a 9V supply, which IMHO is awful small for 12.6V connection (go ahead and try it) yet too much for 6.3V connection (tube life will be hundreds of hours, and grid emission may be a problem). You gotta drop, but the more you drop the more you need big resistors. So shoot for the 6.0V-6.3v range.

Do NOT worry over-much about heater voltage within 10% of 6.3V. Tubes are NOT expensive. A $20 12AU7 really should last 10,000++ hours. If a little over-voltage reduces that to 5,000 hours, you are paying half a cent per hour for tube replacement. Even if you manage to burn-up a whole $200 tube-amp set in 5,000 hours, just a cew cents/hour. How much is your music worth to you?

(This is all for oxide cathodes, the only kind you are likely to meet. When you get into battery power beach-radio tubes, or 5,000 volt transmitter tubes, you get into different sorts of filaments with a lot less leeway. We used the heater voltage to turn-down battery radios before volume controls were practical. You would run a 833A tube on 10.0V as exact as possible for a few hundred hours, then turn-down 0.05V every day until your 1,000 Watt transmitter could barely hold 999 Watts, then turn back a bit. But that's a different technology and economics than where you are at.)

[lowend]

Thanks for the info. Yeah valves are cheap per hour of use but they are 1/4 as cheap in New Zealand and I'm a cheap bugger to boot. Music is indeed priceless.

Just to save any confusion for a total noob looking at this, a 12V supply is connected as per the stock schematic, plates in series, and yields 6V per heater plate. I'm having to modify the vero to accomodate the bank of resistors and a parallel conneciton of the valve plates using the pin9.

So it's not quite a standard valvecaster shopping list.