Bose, no need to say more - LOL!
wg_ski,
Light show at home? Okay ...
I agree. The industry has sold people a bill of goods. Remember the speakers of the 1960's and 1950's? Large and efficient, plus had great frequency response. They didn't handle a lot of power because they didn't need to. A 50 watt amplifier was HUGE! Today small bookshelf speakers are too big (yeah, right!).
My first big amp was a Bogen Challenger CHA-75. Four output (6AV5?) tubes. I rebuilt it from scrap being used for parts. It still had the transformers so I figured it was worth it. I would sit in the back yard and bounce the music off the woods about 300 feet away and back using a 4 x 10" cabinet. Maybe it didn't sound great, but it was better than most music systems (except my dad's Marantz 2240). But it was loud, and it was magic! It had lots of bass compared to smaller systems.
Running a night club on a tube amp? Okay. Expensive I would think.
Anyway, most higher powered tube amps run 400VDC +, 6BQ5 deals maybe 330 VDC. Iffy 6L6GC tubes have issues above 450 VDC, and a Fender Twin will sort them out (~475 VDC)!
wg_ski,
Light show at home? Okay ...
I agree. The industry has sold people a bill of goods. Remember the speakers of the 1960's and 1950's? Large and efficient, plus had great frequency response. They didn't handle a lot of power because they didn't need to. A 50 watt amplifier was HUGE! Today small bookshelf speakers are too big (yeah, right!).
My first big amp was a Bogen Challenger CHA-75. Four output (6AV5?) tubes. I rebuilt it from scrap being used for parts. It still had the transformers so I figured it was worth it. I would sit in the back yard and bounce the music off the woods about 300 feet away and back using a 4 x 10" cabinet. Maybe it didn't sound great, but it was better than most music systems (except my dad's Marantz 2240). But it was loud, and it was magic! It had lots of bass compared to smaller systems.
Running a night club on a tube amp? Okay. Expensive I would think.
Anyway, most higher powered tube amps run 400VDC +, 6BQ5 deals maybe 330 VDC. Iffy 6L6GC tubes have issues above 450 VDC, and a Fender Twin will sort them out (~475 VDC)!
You have to consider the standard voltage rating values of PSU capacitors: 250 V, 350 V, 450 V, 600 V. Have 15% or 20% safety margin. So for a 450 V capacitor I would use 375 to 400 V raw HV. Then consider the tube specs, maximum anode voltage (= 2x idle voltage) and idle current, power rating.
Or simply have a look at a well proven commercial amplifier.
Or simply have a look at a well proven commercial amplifier.
Many outputs run 75% or so of their maximum ratings. Of course you have recommended design maximum (which is what we mostly use), absolute maximum and intermittent service on some tubes.
For supply capacitors, it is nice to have a 20% margin, but many commercial designs run them closer than that. Guitar amps especially.
For supply capacitors, it is nice to have a 20% margin, but many commercial designs run them closer than that. Guitar amps especially.
Unfortunately 450VDC capacitors (std radials, which is the volume market) has dropped since Covid19, compared to 400VDC. Now you have a maximum of 1500uF at 450VDC as to 2400uF with the use of 400VDC. There is almost 30%-40% less stock (values) with 450VDC and its getting worse.
The KT88 (KT77 & KT88 made by GEC/MOV Hammersmith factory) beam tetrode RCA patent in response to Mullard (Philips) EL34 (6CA7 & KT77 eq.)
Normally the beam tetrode is more expensive than the pentode, For me the compactness and fan cooling tunnels have been adopted to the straight
El34 as compared the wider 6CA7.
The KT88 (KT77 & KT88 made by GEC/MOV Hammersmith factory) beam tetrode RCA patent in response to Mullard (Philips) EL34 (6CA7 & KT77 eq.)
Normally the beam tetrode is more expensive than the pentode, For me the compactness and fan cooling tunnels have been adopted to the straight
El34 as compared the wider 6CA7.
Yes : 450VDC is a completely valid approximation, @Perry Babin.
Considering guitar amps, it would be in the range of 450VDC (40-50W amps) to 500VDC (75-100W amps) with tubes like 6L6GC, EL34, 7027A, KT88, 6550, depending also on the number of tubes.
For Hi-Fi, with similar tubes, it's nearly the same... Sometimes a bit higher to achieve low THD at the given power, which is much less a concern for guitar amps !
For examples :
- My Leak Stereo 60 was at 430-440VDC in Ultra-Linear, Cathode bias operation of an EL34 duet, for 30W output.
- My 75W Audio Research D76 (1974) shows 575VDC on 6550 duet plates, 350-360VDC on 6550 screens.
- An Ampeg SVT bass amp reaches 650VDC plate and 400VDC screen for its 6550 sextet, pouring at least 300W output.
- An Ashdown BTA-400 bass amp even shows 680VDC on KT88 octet plates for 400W output.
- My 70s SF Fender Twin reverb has 450-460VDC plate and screen on 6L6GC quartet, which is the norm for BF, SF and RI models.
- Nearly all Marshall 100-Watters are 450-470VDC plate and screen for their EL34 quartet, sor are the Hiwatts.
T
Hi HowardJohnstone,
Sorry, but I have to ask. Why do you need such silly high values of capacitance? It doesn't buy you anything at all. Heck, 100 uF is very high unless you're running bank of KT88 or higher dissipation tubes.
If you're single ended, there are other ways to drop hum level, but you're already behind the 8-ball there.
Sorry, but I have to ask. Why do you need such silly high values of capacitance? It doesn't buy you anything at all. Heck, 100 uF is very high unless you're running bank of KT88 or higher dissipation tubes.
If you're single ended, there are other ways to drop hum level, but you're already behind the 8-ball there.
First of all, you really do need to regulate B+ if you are trying to get away with 400VDC. Just 10% mains variation would give 440V alone, another 5% for
transformer regulation under light load etc. Therefore we see the use of series capacitors, chokes and resistors LC-filters) make up the rest. Now that the
HIP5600 is long since gone, The problem with LM317 is the minimal load (Maida regulator). (The capacitance values where just for comparison, but you will find the same relation at the 100-200 uF level.)
transformer regulation under light load etc. Therefore we see the use of series capacitors, chokes and resistors LC-filters) make up the rest. Now that the
HIP5600 is long since gone, The problem with LM317 is the minimal load (Maida regulator). (The capacitance values where just for comparison, but you will find the same relation at the 100-200 uF level.)
Hi HowardJohnstone,
True, but high values of capacitance does nothing to regulate mains variations at all. Yes, we definitely need headroom in filter capacitors. Most to the bone tube designs relied on the capacitor manufacturer's safety margin. Then our mains voltage was raised over the years.
I have long used discrete regulator designs. They are often more reliable in the long term anyway.
True, but high values of capacitance does nothing to regulate mains variations at all. Yes, we definitely need headroom in filter capacitors. Most to the bone tube designs relied on the capacitor manufacturer's safety margin. Then our mains voltage was raised over the years.
I have long used discrete regulator designs. They are often more reliable in the long term anyway.
In defense of SE amplifiers,...
Almost every console stereo sold in the US , or Germany was SE in the 50s and 60s, until the component systems and Japanese stereo systems displaced them. A short list of companies include Telefunken, Grundig (EL84), Magnavox, RCA, Fisher, Emerson and Sears (6BQ5 and 6V6). The reason they sounded as good as they did (for SE amps) is that they were systems with the amps matched to the speaker systems. The speakers were highly efficient, allowing the low power systems to operate with modest distortion.
If one is going to use an SE amp and expect low distortion (with the possible exception of GM-70 tubes and the like), one needs to select fairly efficient speakers that work well with the dampening factor and power level of the amp. I have both Klipsch Heresy and Klipsch Heresy II speakers as well as a set of Kenwood KL-5050 speakers. All three sets of speakers are in the 98dB/W range. All three sound good with 6W SE amps, because at normal listening levels the power level is only 32mW with peaks of less than 1W. This means that the 2nd harmonic is below -80dB and third and successive components are below -100dB.
Almost every console stereo sold in the US , or Germany was SE in the 50s and 60s, until the component systems and Japanese stereo systems displaced them. A short list of companies include Telefunken, Grundig (EL84), Magnavox, RCA, Fisher, Emerson and Sears (6BQ5 and 6V6). The reason they sounded as good as they did (for SE amps) is that they were systems with the amps matched to the speaker systems. The speakers were highly efficient, allowing the low power systems to operate with modest distortion.
If one is going to use an SE amp and expect low distortion (with the possible exception of GM-70 tubes and the like), one needs to select fairly efficient speakers that work well with the dampening factor and power level of the amp. I have both Klipsch Heresy and Klipsch Heresy II speakers as well as a set of Kenwood KL-5050 speakers. All three sets of speakers are in the 98dB/W range. All three sound good with 6W SE amps, because at normal listening levels the power level is only 32mW with peaks of less than 1W. This means that the 2nd harmonic is below -80dB and third and successive components are below -100dB.
I hope everybody has the chance to hear, and enjoy listening, to good stereo amplifiers that have one or more of the following characteristics:
single ended
single ended parafeed
push pull
OTL
All with . . .
no negative feedback
local negative feedback
global negative feedback
nested negative feedback
If you have not . . . get out of your house/apartment more often, and go to hi fi shows, audio clubs, dealers, friends, etc.
(If you have not heard good examples of all of these amplifiers, your education has been sadly neglected).
single ended
single ended parafeed
push pull
OTL
All with . . .
no negative feedback
local negative feedback
global negative feedback
nested negative feedback
If you have not . . . get out of your house/apartment more often, and go to hi fi shows, audio clubs, dealers, friends, etc.
(If you have not heard good examples of all of these amplifiers, your education has been sadly neglected).
Considering your list, @6A3sUMMER, here are my matching items - more or less :
single ended :
single ended parafeed = ⁉️
push pull :
OTL :
All with . . .
no negative feedback = U-300B, U-OTL
local negative feedback and global negative feedback = U-KT120, The MICRO-AMP
nested negative feedback = Audio Research D76
T
single ended :
single ended parafeed =
⁉️push pull :
OTL :
All with . . .
no negative feedback = U-300B, U-OTL
local negative feedback and global negative feedback = U-KT120, The MICRO-AMP
nested negative feedback = Audio Research D76
T
Fixed every kind of amp. Heard them all from many various manufacturers.
As I said. What you like the sound of is fine. What is low distortion is rather specific, same for low noise.
One thing that is factual. Even in the early 1930's, the best equipment was push - pull. This trend was consistent through the 1960's. Table radios (except a very few) were single ended, phonographs (again except a very few) were single ended. These were on the low end of cost. Only when snake oil became more predominant did we see expensive single ended equipment.
However, if you do prefer this type of gear (or OTL) - fantastic. This is a valid preference.
As I said. What you like the sound of is fine. What is low distortion is rather specific, same for low noise.
One thing that is factual. Even in the early 1930's, the best equipment was push - pull. This trend was consistent through the 1960's. Table radios (except a very few) were single ended, phonographs (again except a very few) were single ended. These were on the low end of cost. Only when snake oil became more predominant did we see expensive single ended equipment.
However, if you do prefer this type of gear (or OTL) - fantastic. This is a valid preference.
