If you read Gillespie's details about the EFB system, it's designed to follow/track any PS sag and hold proper bias/operating conditions regardless.
It works well with my amp, and my amp doesn't need or require massive capacitors, something people have seemingly gone nuts about.
^^^
This!
PLUS large electrolytics put a strain on your transformer and creates spikes well into the RF. Far better to use moderately sized electrolytics and use a choke. And when using solid state recctifiers use hash filters.
Valves bought in 'bay is probably dissimilar. Valved bought as matched from
a serious vendor is similar, they don't need individual adjustments.
EL84 is available in new production and as such may be matched to any
degree of accuracy.
I came across 4 excellent original 7189A's a while back.
Radio Shack branded "gold pins" "Lifetime" tubes.
These are a heavy duty version of the 6BQ5/EL84's, and withstand higher voltages and currents, and thicker bottles.
They should last me decades in my RCA Victor stereo console, running at 300V B+.
And they sound wonderful too.
Radio Shack branded "gold pins" "Lifetime" tubes.
These are a heavy duty version of the 6BQ5/EL84's, and withstand higher voltages and currents, and thicker bottles.
They should last me decades in my RCA Victor stereo console, running at 300V B+.
And they sound wonderful too.
Recently was reading a datasheet (IIRC) on one of their long life tubes (10 000 hour) and that mentioned that if you wanted real long life out of them and stability (no wandering of values) then to run them at 30% less load on the plate. I like the 5670, they can go for long times without plate voltage and if run properly they can last 100 000 hours. Very linear and very robust, used in the early analog computers, tanks, jet fighters etc. . Above all they are still relatively cheap. IIRC also used in the El Cheapo amplifier.
The 6P14P-ER is a good alternative to the 7189A but is getting scarce and pricey. I've bought some 6P14P-EV's and some used Tesla's. A pair of Tung Sol 6BQ5's held up well but I had three Tung Sol 6V6 go bad on me during the last two years. The 6BQ5 were run above their ratings (about 13 Watts) but the 6V6 were well inside their ratings. Mind boggles.
Time to make an adapter for my Dyna-Quik 500 tube tester and test all the 6BQ5's I've been buying.
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What does a tube do when it goes bad? Is it a visual thing? Or does it start to get noisy? Distortion performance reduction?
The watts out get low, on output tubes. You can measure the lack of wattage on a speaker with an analog AC voltmeter. Usually the first thing causing low watts is B+ (plate voltage) sags with attempted high watts. But if caps & rectifier are good and plate voltage is stiff, and still not enough current will come out to produce rated watts, change the output tubes.
On 6CA7 and 2000 hours/year, I used to get about 6-8 years out of a set of them. Many of those hours were silent, I had read that heating up & cooling off tubes (power cycle) caused failures too.
I never wore out a set of 7199's in 10 years of daily use. These were combined driver & phase splitter tube. Did wear out rectifier tubes.
On 6CA7 and 2000 hours/year, I used to get about 6-8 years out of a set of them. Many of those hours were silent, I had read that heating up & cooling off tubes (power cycle) caused failures too.
I never wore out a set of 7199's in 10 years of daily use. These were combined driver & phase splitter tube. Did wear out rectifier tubes.
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Please, that claim of failures due to heating/cooling is an internet myth, and you along with others that believe that should forget about it.
Forget you ever heard it.
I've got tubes here dated 1962, 1963, that are in fine condition, being used in products from the same era - which were "turned off and on" countless times through the decades.
I've also worked on 1920's to 1950's radios, etc, with original tubes that are fine.
Yes, occasionally a tube goes bad - always happened through the years - it's normal manufacturing issues, and/or operating conditions determined by the under-chassis components.
That's one reason that tubes were made to "plug in" to sockets in the first place.
With due respect: It depends.
At one stage I had a vacuum coater for telescope mirrors and used a tungsten wire that would heat up and evaporate the material that needed to be deposited on the mirror.
If the element was heated up too fast it would last less than a dozen times, when it was heated slowly it would last almost a hundred times.
I wonder how many current day designs use NTC's across the primary of a transformer so that the filaments do not light up like a flash bulb (like used for taking a picutre when we commonly used film).
If you read some of the datasheets then you'll notice that some tubes' datasheets state that the tube has a life expectancy of xx hours and it is assumed that the tube is not switched on more than y times per day.
It is my view that if a tube's filament, of those tubes that have not been designed to be switched on or off all the time, is exposed to sudden large inrush current that then that tube will suffer early demise.
I've also found that this appears to happen more with filament voltages that are at the high end of the allowed range for the flament voltage, if not exceeds it.
And to reply....
First thing, your tungsten vacuum coater is not anything like a vacuum tube.
Additionally, I've no need to consult vacuum tube datasheets, I'm aware of tube life, controlled warm-up times, and operating conditions.
After servicing literally thousands of tube-type consumer products over the decades, I hold firm on by own experience and beliefs.
Finally, I'm sure there's plenty of "modern day" designs that suffer from poor design, and needing "helper" components like NTC's and such.
It's my experience that they were never needed before in all those products that I've serviced.
Ya gotta amp, etc, that somehow needs those NTC's? - blame the design on the critter that made it.
Thank you for calling me a critter. And well done that you have been able to memorize the tens of thousands tube datasheets.
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Thank you to everyone for your input. I feel like I will get a far better result in the end because of the discussion in this thread! So thanks to everyone. Ended up going with the amp schematic posted by Wise old tech because I have 12AX7s on hand so that fit perfectly.
Again this is really the first real attempt I have made at just about any electrical project so I am coming off a skill level of zero. Planning and execution are not my strong point but that said..
To amp board, power board and EFB board are all built. There is even a small offshoot from the 6.3v source to power some LEDs to illuminate the amp under operation and to act as a power indicator. Waiting on transformers to arrive from the USA and I will start mounting everything to the chassis when they arrive.
Had a lot of fun with this and it looks like this will be a lifetime of learning and discovery!
Again this is really the first real attempt I have made at just about any electrical project so I am coming off a skill level of zero. Planning and execution are not my strong point but that said..
To amp board, power board and EFB board are all built. There is even a small offshoot from the 6.3v source to power some LEDs to illuminate the amp under operation and to act as a power indicator. Waiting on transformers to arrive from the USA and I will start mounting everything to the chassis when they arrive.
Had a lot of fun with this and it looks like this will be a lifetime of learning and discovery!
