We got a measured output at clipping of 4.9W for our RH-84 variant build.
The A10 (EL34) has to be running as a pentode (or UL) to get that kind of power (5-7w)
dave
Output impedance (AKA damping factor (DF)) and while you could measure it or have it measured, normally one just asks the manufacturer and really should be part of its specs, though sadly, too often not and why folks often keep trying different tube amps to get the best sound, one need only know what likely works best with 'X' speaker or if one has 'deep pockets', can buy a separate preamp, amp or receiver with variable (DF) like we used until the solid state (SS) era.
Nice room and a sloped ceiling, a big + acoustically and shallow enough not to need a lot of efficiency unless like to play recordings that are very dynamic, such as some symphonies, pipe organ and even large choirs; ditto many action movies.
I am very clearly out of my depth here, but I do know that it is being run UL. As far as asking the manufacturer for the output impedance, they'd give an answer that's probably a worse guess than mine.
You all are correct, its an EL34, not an EL84, I was a bit distracted posting earlier, my apologies.
I have no clue about global negative feedback and would need to learn more to be able to answer from the schematic.
Seems I have quite a lot more to learn. I ended up pulling the trigger on the amp. $300 delivered was hard to argue with, even if its going to be a kit/science experiment. I'll be much more inclined to learn by having something to work on and look at. I have the cabinets from the HH Scott to mess around with until I can arrive at some decent permanent solution.
Planet 10, you make a great point about buying subs vs not. I'd much prefer not too for a multitude of reasons.
You all are correct, its an EL34, not an EL84, I was a bit distracted posting earlier, my apologies.
I have no clue about global negative feedback and would need to learn more to be able to answer from the schematic.
Seems I have quite a lot more to learn. I ended up pulling the trigger on the amp. $300 delivered was hard to argue with, even if its going to be a kit/science experiment. I'll be much more inclined to learn by having something to work on and look at. I have the cabinets from the HH Scott to mess around with until I can arrive at some decent permanent solution.
Planet 10, you make a great point about buying subs vs not. I'd much prefer not too for a multitude of reasons.
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Well, if you use a max flat speaker design and it measures/sounds like it has a 'smiley face' response from using tone controls to boost the low and high ends with just the mids 'flat', it has a high output impedance.
In an attempt to educate myself I've been reading the past couple of hours and have at least come across some answers to y'alls questions.
This thread has a more granular description of the mods I was speaking of before by the person who posted the youtube videos I saw. It's a long read and I don't expect anyone to actually read it, but it's been interesting as a complete novice with this stuff.
There is apparently no negative global feedback. Skunkie was nice enough to include before and after schematics of all the mods. I obviously don't (yet) understand the theory behind them, but I do trust the measurements presented in the videos and the thread. As far as speaker selection I'm still in the weeds but it will get sorted. I havent mentioned yet but I broke my heel bone a couple weeks ago, so I have much more time to read/research than I'm normally used to 🤣
Edit: That's not quite how I expected my link to show up
This thread has a more granular description of the mods I was speaking of before by the person who posted the youtube videos I saw. It's a long read and I don't expect anyone to actually read it, but it's been interesting as a complete novice with this stuff.
There is apparently no negative global feedback. Skunkie was nice enough to include before and after schematics of all the mods. I obviously don't (yet) understand the theory behind them, but I do trust the measurements presented in the videos and the thread. As far as speaker selection I'm still in the weeds but it will get sorted. I havent mentioned yet but I broke my heel bone a couple weeks ago, so I have much more time to read/research than I'm normally used to 🤣
Edit: That's not quite how I expected my link to show up
Attachments
I thought I saw you posting in there. I'll need to read it a fair few times more to start to understand it but eventually...
Don't pay any attention to my posts. They could be utter nonsense. 😉
jeff
jeff
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First thing i notice in the maps posted was the loss of the paralleled ECC83, my next step would be swap it with somwthing beefier,
Replacing at least the last capo in the PS w a poly also
dave
Replacing at least the last capo in the PS w a poly also
dave
In the original amplifier, the biasing is completely screwed up - one should follow the operation point recommended by data sheet, which the designer didn't do. That's why the amp has terrible distortions and low power output. Skunkie corrected the op. point - this should bring real improvement.
The amp doesn't have global NFB. UL connection provides some local feedback, which gives damping factor of about 2, not good from standpoint of electric damping. Skunkie adds another local feedback, a resistor from EL34 plate to 12AX7 plate. This is called Schade feedback. Together with UL, it will bring DF to something like 4-6. In enclosure design, real Qe will be a little more than in data sheet.
Skunkie mod or alike is a must for this amp to have acceptable performance.
The amp doesn't have global NFB. UL connection provides some local feedback, which gives damping factor of about 2, not good from standpoint of electric damping. Skunkie adds another local feedback, a resistor from EL34 plate to 12AX7 plate. This is called Schade feedback. Together with UL, it will bring DF to something like 4-6. In enclosure design, real Qe will be a little more than in data sheet.
Skunkie mod or alike is a must for this amp to have acceptable performance.
Generally these amps are junk - they have poor quality output and power transformers and constructed as cheap as possible. They make them look good, but if one looks at how they can be improved, it turns out that everything has to be scrapped and done from scratch.
Re caps; since you're using tubes there's a certain synergy using PIO caps, not to mention technically better if modern ones haven't improved much since this testing was done.
No. I've owned Chinese valve amps that were very good.
The one you (o/p) mention piqued my interest at one point. I ended up buy a used British built amp in mint condition.
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