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I'm wondering if the 845 should be an 'Afterburner' stage. For example, build a two stage 2A3 amplifier which can driver speakers at low power, then switch on the 845 afterburner driven by plate of 2A3 for big music
Turbo mode
Another thought is to have 2 power settings for the 845. One for full power where you'd dissipate about 90w and a lower power where you could dissipate much less. On the low power settings the 845s would last for ever.
That's a novel idea, though you'd be buying 4 output transformers rather than 2.
Another thought is to have 2 power settings for the 845. One for full power where you'd dissipate about 90w and a lower power where you could dissipate much less. On the low power settings the 845s would last for ever.
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I shouldn't have written 'speakers' as I'm going to be building mono. My main system is only one big speaker. I find many benefits with this approach: no worry about the sweet spot for listening, far fewer room interaction issues to deal with, many recordings are not properly recorded and mixed for stereo and can sound false to my ears, not fighting the room by trying to impose the 'recording venue' onto it but allowing my room to be itself, no issues with channel matching for gain or volume pots etc., plus speaker placement is far more flexible - for me there are zero downsides in terms of listening pleasure, and you can focus your resources. So only 2 output transformers.
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You will likely find them at lower price there. But selecting and testing? I am not sure. If you can get them tested with good equipment then go for it. Buying Chinese tubes untested is a no no for me....
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You might find a bargain if you just want one. Most people want an identical pair. There may well be orphaned 845s out there. Why not ask on the Parts forum?
I don't think I have the energy to make an 845 amp, but I do want to get my hands on an old, worn out 845 some day with an intact filament to make into a desk lamp...
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good - we can split a pair and you get an expensive desklamp and I get a niceamp 😀
No every seller tests the tubes he sells. Some do, some simply sell them as factory tested and some nothing at all. However factory tested tubes have rather high tolerances unless specified.
Some years ago I bought a pair of 2A3B when they first came on the market. Factory tested and matched, it said on the box, but when I put them on my Hickok they only show 3 mA/V. If I measure the filament current @2.5V (regulated) this is only 2.2A. Output power is 70% of that I get from a lightly used NOS 2A3.....
I think people should stop thinking about watts...
I measured the peak voltages on a 2 way driven to comfortable levels in an ok room...
It was at most 1.5Vrms into 3 ohms at the worst possible scenario, average is around 0.7Vrsm into 6 ohm.
Note that at this level the woofers are used to their maximum linear excursion...
But, I can easily tell the difference with triodes, low power amps, high power amps. Something else than raw power makes the difference.
For 845, 811 etc, the KEY is to handle the impedance variation, get a proper damping.
8 Watts is enough to rock 82db sensitive speakers if done properly.
I measured the peak voltages on a 2 way driven to comfortable levels in an ok room...
It was at most 1.5Vrms into 3 ohms at the worst possible scenario, average is around 0.7Vrsm into 6 ohm.
Note that at this level the woofers are used to their maximum linear excursion...
But, I can easily tell the difference with triodes, low power amps, high power amps. Something else than raw power makes the difference.
For 845, 811 etc, the KEY is to handle the impedance variation, get a proper damping.
8 Watts is enough to rock 82db sensitive speakers if done properly.
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Sakuma says "Many Japanese audiophiles use high power amplifiers to get powerful mid-range and bass. But excellent speakers, like the Lowther and Altec, refuse brute power.
The most important goal is not 'Power', but 'Energy' and 'Frame of tone'...".
I have a Hammond 1629SEA output transformer available for this purpose. Provides 6.5k nominal impedance when driving 8 Ohm. I think this is a good marriage for the 845.
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no, you need 10k , 8 k minimum, or else you need to aim for lower bias,
good news Bigun,,,, it is suitable for a B+ of 450V + SV811-3 in A2 (bias 60ma)===)) 6L6 + Interstage , with around 4db of GNF you will send to graveyard all the 300B amps.
its going to be a safer 845, with I am ready to bet, as good performance.
I did a research , for IT use this : LL2746
For bias, use a regulator , the sv811 can swing 1000V pp into 6k-8R
this is 350Vrsm*2/6k=20 watts at least
good news Bigun,,,, it is suitable for a B+ of 450V + SV811-3 in A2 (bias 60ma)===)) 6L6 + Interstage , with around 4db of GNF you will send to graveyard all the 300B amps.
its going to be a safer 845, with I am ready to bet, as good performance.
I did a research , for IT use this : LL2746
For bias, use a regulator , the sv811 can swing 1000V pp into 6k-8R
this is 350Vrsm*2/6k=20 watts at least
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I am itching to buy an 845 ! and I noticed that Sakuma San used a plate load of 5K and he spent many years exploring the 845 so maybe the 6.5k will be fine
for the interstage I have some Hammond 126B which I have read are good performers
I haven’t decided on a drive a tube but why not a 2a3
for the interstage I have some Hammond 126B which I have read are good performers
I haven’t decided on a drive a tube but why not a 2a3
Why not triode strap a 6AV5GA or if you want to save money a triode strapped 6P1P? 😀
I can't say I've ever heard a single ended tube amp that was more than ECL82 or ECL86, but I love triode strapping sweep tubes in push pull.
You can always configure the 845 for lower power versus higher power. Have a switch to drop the pate and filament a bit and rebias appropriately. I have done that for years.
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lower power ? - let her fly apart !
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OTOH, I think you’re right, it may also be a waste of a 2nd OPT
I've little experience with that approach - but the best sound I've yet heard from a SE amp was a triode strapped sweep tube on an experimental chassis. A russian sweep tube driven by 6C45P via a Hammond 126B.
sakuma San liked to use the KT 66 triode wired, which of course is very linear, and he and others have also said that the driver tube is a big part of the sound so it has to be chosen carefully. A 2A3 (or 45) might be just the ticket, then it’s all DHT at the output
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OTOH, I think you’re right, it may also be a waste of a 2nd OPT
I've little experience with that approach - but the best sound I've yet heard from a SE amp was a triode strapped sweep tube on an experimental chassis. A russian sweep tube driven by 6C45P via a Hammond 126B.
sakuma San liked to use the KT 66 triode wired, which of course is very linear, and he and others have also said that the driver tube is a big part of the sound so it has to be chosen carefully. A 2A3 (or 45) might be just the ticket, then it’s all DHT at the output
You know what's ridiculously linear? A pentode with a CCS plate load and a little shunt feedback. My DHT driver in my Unity-Coupled amp is pretty linear up to high levels but generates way more high-order distortion than a humble EL34 or EL84. I'd use one of those to drive an 845.
OP here,
Perhaps I can shift the discussion a little and ask what you’ve found to be the nicest sounding 845, 211, etc. amp.
Perhaps I can shift the discussion a little and ask what you’ve found to be the nicest sounding 845, 211, etc. amp.
This is a nice sounding amp and can be done except for some "bells and whistles"....
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6.5K is a good load to play with 750-800V plate voltage for good 12-15W. Driver tube use a 10Y if you fancy same type of filaments etc. otherwise the amp in the link above is a two stage amp with the high gain 6HV5A (or equivalents). The latter with its mu=300 allows a straight 2-stage amp.