The plate supply in this amplifier is well in excess of 1KV, and so those caps are very likely to 450V or 500V caps stacked in series. The inrush currents at power on are somewhat reduced by the slow start circuitry but will still be significant when the relay closes - I would not increase the overall capacitance before the choke too significantly if at all, post choke I might consider doubling it and adding a good 2KV film cap of a couple to ten or so uF to improve HF decoupling performance, if necessary to control q I would add an ohm or two of resistance in series with this cap. (In case the electrolytics are excessively inductive and you end up with a resonant circuit.) Good quality switching supply capacitors from Panasonic, Rubycon or similar are ideal. Look for ones with low esr/esl and da, they'll behave better at high audio frequencies - you might want to look up the ones fitted if possible, no point in replacing them with something that is no better specification wise.
I would not assume the output transformers are bad, there tends to be a lot of labor content in these relative to material cost, and this is one area where attention to detail and low labor costs might still pay off. (My experience with Chinese output transformers so far has been positive, generally it's the place where they put the most effort and expense.)
Replace the cathode bias bypass cap in the first stage with an inexpensive black gate..
Coupling caps, and input circuitry simplification will net you big gains, ditch the source selector switch and volume pot and go straight in with an appropriate grid stopper (say 1k) and a 100K grid bias resistor. These changes alone may net you an improvement in stereo separation and hf extension.
I would not assume the output transformers are bad, there tends to be a lot of labor content in these relative to material cost, and this is one area where attention to detail and low labor costs might still pay off. (My experience with Chinese output transformers so far has been positive, generally it's the place where they put the most effort and expense.)
Replace the cathode bias bypass cap in the first stage with an inexpensive black gate..
Coupling caps, and input circuitry simplification will net you big gains, ditch the source selector switch and volume pot and go straight in with an appropriate grid stopper (say 1k) and a 100K grid bias resistor. These changes alone may net you an improvement in stereo separation and hf extension.
dantwomey said:
Decades ago there was too much SE amp rabble.....(for what ?) the fact that youv'e spotted the flaws in the amp sound so soon after purchasing it isn't good news for any SE manufacturer. you mention are new to tube amps. The audible difference must be large.
I don't work with +1kV anymore, it just isn't worth the xrays and for most DVM multimeters is too hign for the hassle. I get just as good/better sound with so simple UL-p-p stages working a fraction of the voltage. And what to do with the remains....ebay the chassis and start reading up ?
There's alot of talent in this forum......use it
richj
I would try some tube rolling first before venturing into cap replacment (or even wholesale circuit modifications). If those truly are 6L6s driving the 845 - it won't cost too much to try some different 6L6GCs/5881s or KT66s in there...
Does the 6J4P have an Euro/American equivalent? like a 6SJ7? That would also be worthwhile to try. I'm not saying this will cure the ills you perceive, but it might be worth trying.
Does the 6J4P have an Euro/American equivalent? like a 6SJ7? That would also be worthwhile to try. I'm not saying this will cure the ills you perceive, but it might be worth trying.
Dan# Did you feel the SE didn't have enough poke
Are you using lo sens LS i.e below 87dB/w sens which would cause the amp to strugggle ? ...i.e have you tried different speaker systems to compare ?
Looking at comments made by Morrison Dinosaur (Sound Practices spring 1994), quote;
1 Big triodes tend to have great bass but dark upper midranges and treble. (Ignore the tube manuals suggested points)...oh ??
2. High and medium power tubes are very driver stage dependent.
3. Interstage transformer.....another awkward item.
The rest of the issue to's & froes with other power triodes.
From looking at the loadline, at approx 500V B+; 3K anode Z; the 845 plate I at 90mA would tickle roughly 5.5 Watts into 6-8Ohm LS.
To me despite a lumpy psu to supply the heat, that amp o/p 's 'a bit'skinny.... am I correct ?
richj
Are you using lo sens LS i.e below 87dB/w sens which would cause the amp to strugggle ? ...i.e have you tried different speaker systems to compare ?
Looking at comments made by Morrison Dinosaur (Sound Practices spring 1994), quote;
1 Big triodes tend to have great bass but dark upper midranges and treble. (Ignore the tube manuals suggested points)...oh ??
2. High and medium power tubes are very driver stage dependent.
3. Interstage transformer.....another awkward item.
The rest of the issue to's & froes with other power triodes.
From looking at the loadline, at approx 500V B+; 3K anode Z; the 845 plate I at 90mA would tickle roughly 5.5 Watts into 6-8Ohm LS.
To me despite a lumpy psu to supply the heat, that amp o/p 's 'a bit'skinny.... am I correct ?
richj
richwalters said:
My speakers are in the mid 90's db and this amp has plenty of poke. I think it all boils down to preference. Although my SS can be a bit sterile it's treble detail, air, is excellent. It's soundstage depth and detail are superb. And, it's got a clarity and detail overall that I don't want to give up. Perhaps tubes aren't for me?
Regards,
Dan
Output stage B+ is over 1KV... (820Vrms secondary) Output power for this design is supposed to be in the range of 20W. (No A2 operation)
Tubes can provide all the air and detail you want or expect, it is a matter of design quality and execution. This was a very inexpensive amplifier before you factor in the shipping expense.
Tubes can provide all the air and detail you want or expect, it is a matter of design quality and execution. This was a very inexpensive amplifier before you factor in the shipping expense.
kevinkr said:
You couldn't be more correct. I put in a very low bid not expecting to win. When I did win I honoured the sale. When you consider the cost before shipping ($295USD) this is an exceptional amplifier. Once again, in its current state it doesn't suit my taste.
Looking to the future again. If I choose to sell it I will probably spend alot more on a kit recommended by my forum members.
Regards,
Dan
Think about PP rather than SE. A well implemented PP can better an SE and will more than likely save you money.
Think about the Vacuum State 300dba. To my mind this is the best kit availble and it will stagger with it control over bass and treble. I have messed with the design idea's in this amp and it delivers all that Valves have to offer - with no penalties over SS.
Shoog
Think about the Vacuum State 300dba. To my mind this is the best kit availble and it will stagger with it control over bass and treble. I have messed with the design idea's in this amp and it delivers all that Valves have to offer - with no penalties over SS.
Shoog
Have you measured what it's doing up top? Before making any decision I would confirm it's not a matching issue or amp flaw.
My SE homebrew is flat into an 8 ohm load past 50 kHz. Into typical speaker loads it should have a rising response up high. It still sounds dark compared to the solid state I hear at work all day. However just two days ago I wondered who was whistling outside my window. It was Beck. Preference, expectation and natural presentation aren't always in alignment.
My SE homebrew is flat into an 8 ohm load past 50 kHz. Into typical speaker loads it should have a rising response up high. It still sounds dark compared to the solid state I hear at work all day. However just two days ago I wondered who was whistling outside my window. It was Beck. Preference, expectation and natural presentation aren't always in alignment.
rdf has a valid point, if you have been listening to solid state for a long time you might just have to listen beyond the perceived lack of highs and see what is really there. You might be surprised.
In younger days I found ss excruciatingly bright and realized that there was no more real detail than present in the signature sound of a much darker sounding tube amp I had.
I was and still am pretty much of an accuracy freak, I want to hear what is in the recording, and I have the expectation the system will sound like the recording, not live music. I guess I should mention my tastes range from techno to classical and pretty much anything in between.
Incidentally I went from solid state to push pull tubes to SE in that order, and I won't be going back. I find the level of detail, tonal accuracy, and dynamics of a properly designed SE hard to beat, if you are on a budget and/or want to follow dogma rather than solid EE design principles regardless of topology choices made - PP is far more likely to yield acceptable results. AND it is very important that the amplifier whether SE or PP be designed to drive the speakers it is most likely to be used with (or alternately design speakers to use with the amp depending on POV)
Just my point of view.
In younger days I found ss excruciatingly bright and realized that there was no more real detail than present in the signature sound of a much darker sounding tube amp I had.
I was and still am pretty much of an accuracy freak, I want to hear what is in the recording, and I have the expectation the system will sound like the recording, not live music. I guess I should mention my tastes range from techno to classical and pretty much anything in between.
Incidentally I went from solid state to push pull tubes to SE in that order, and I won't be going back. I find the level of detail, tonal accuracy, and dynamics of a properly designed SE hard to beat, if you are on a budget and/or want to follow dogma rather than solid EE design principles regardless of topology choices made - PP is far more likely to yield acceptable results. AND it is very important that the amplifier whether SE or PP be designed to drive the speakers it is most likely to be used with (or alternately design speakers to use with the amp depending on POV)
Just my point of view.
kevinkr said:
Interesting, I went the otherway round.. in the 1960's I went from p-p 807's then 1970's to SS then to SE then later to multiple parallel pairs UL p-p and I won't be touching SE ever again !
P.O.V ??..In the real world, an amplifier should drive any coil speaker plonked across it's output terminals, so long same impedance. I can't see any merit <tuning> a particular amp for a speaker.
This implies crossover sensitive phase problems ... Once I repaired a Velleman which are very tricky amps for certain speakers. Not a good stability sign as a power transient can break into oscillation.
richj
Dan,
Since you have no experiance working with tubes or high voltages do not go poking about inside that 845 amp you just purchased. There are voltages in there that will kill you. Since you don't like the sound you should sell it and build a nice tube kit amp to learn something about tubes. I would recommend picking up a Daynaco ST 70 and upgrading it. There are several upgrade kits available. One nice upgrade kit that is available again is the one from Welborne Labs. The kit comes with excellent instructions and everything fits on to a single board which relatively easy to install on the chassis. When you are done you will have very good sounding tube amp with out risking your life.
Andy
Since you have no experiance working with tubes or high voltages do not go poking about inside that 845 amp you just purchased. There are voltages in there that will kill you. Since you don't like the sound you should sell it and build a nice tube kit amp to learn something about tubes. I would recommend picking up a Daynaco ST 70 and upgrading it. There are several upgrade kits available. One nice upgrade kit that is available again is the one from Welborne Labs. The kit comes with excellent instructions and everything fits on to a single board which relatively easy to install on the chassis. When you are done you will have very good sounding tube amp with out risking your life.
Andy
richwalters said:
While from a purely engineering standpoint I completely agree with you, this being the real world, compatibility between any given good speaker system and equally good amplifier regardless of technology used is not assured in my limited experience.
I decided not to rely on the somewhat random probability that my amplifier designs would sound good with a specific speaker so I designed a speaker system to achieve proper damping with amplifiers having low damping factors - read this as high source impedance. This is less of a compromise than it might seem at first as I can always pad the source driving the woofers to maintain the proper driver damping.
Unfortunately it is also my observation that higher order cross-over designs interact in interesting ways with amplifiers that exhibit less than ideal voltage source behavior, and this does effect the phase and frequency response in the driver cross-over region. Depending on cross-over design the effect can be subtle or not so subtle, and this probably accounts for a lot of the interaction between amplifiers and speaker systems. I'm sure this also partially accounts for a lot of the popularity of the full range driver in folded horns, tl and perhaps ob as well with certain pwm amps (T amp) and tube SE amplifiers.
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