5 weeks after my Yarland 34A & Xindac arrived DHL sent me an invoice for £41.36.Re: Re: 300B Tubes
I myself is not a DHT or single-ended fan, but to answer your question in general form: All to often this "dc on heaters" is a pious thought. Folks would rectify heater supplies even for high-current demands as in power amplifiers, add some capacitance, and hey presto! "I have dc on my heaters".
No you have not. Rather you have some dc modulated by a rather nasty ripple with switching rise-times giving more interference than ac would have. To complete, there should be no reason for dc on heaters in main amplifiers.
But in your case of DHF it is all the more important that one does not have nasties on heaters. I have cicuits where designers apparently got away with an adjustable centre tap on ac filaments. If you use dc, the supply must not only be rectified but would need a fairly proper filter to get rid of rectifier artifacts (i.e. a low ripple).
As said a general pointer to something often overlooked. Someone else with experience would be able to enlighten us about what kind of (low) ripple would be needed for hum-free operation of DHTs.
Regards.
andrew_whitham said:Is there any theoretical basis for this do you know, or is it paranoia? yes / no? I'm quite willing to be put right here or at least appreciate the alternative argument. But, it strikes me that a non DHT tube is likely to be more "cost effective"than the alternative.
I myself is not a DHT or single-ended fan, but to answer your question in general form: All to often this "dc on heaters" is a pious thought. Folks would rectify heater supplies even for high-current demands as in power amplifiers, add some capacitance, and hey presto! "I have dc on my heaters".
No you have not. Rather you have some dc modulated by a rather nasty ripple with switching rise-times giving more interference than ac would have. To complete, there should be no reason for dc on heaters in main amplifiers.
But in your case of DHF it is all the more important that one does not have nasties on heaters. I have cicuits where designers apparently got away with an adjustable centre tap on ac filaments. If you use dc, the supply must not only be rectified but would need a fairly proper filter to get rid of rectifier artifacts (i.e. a low ripple).
As said a general pointer to something often overlooked. Someone else with experience would be able to enlighten us about what kind of (low) ripple would be needed for hum-free operation of DHTs.
Regards.
Re; 300b Tubes
All I can say is, for those who don/t know it, the Audion Silver Night is a very high quality amplifier, and there are no hum problems that I know of with the design used, which incorporates a pair of (directly heated) 300B Valves. I guess the DHT vs. KT88/EL34, etc., argument is one of those that will run and run. It's a case of 'chacun a son gout' as they say in France!
All I can say is, for those who don/t know it, the Audion Silver Night is a very high quality amplifier, and there are no hum problems that I know of with the design used, which incorporates a pair of (directly heated) 300B Valves. I guess the DHT vs. KT88/EL34, etc., argument is one of those that will run and run. It's a case of 'chacun a son gout' as they say in France!
Hi,
I have run Audio Research D76 clones for many years - quiet insofar as base noise levels go - lovely - but the GEC KT88s have aged like me and I do not have a closet-full of replacements... I succombed to the hoopla of SE amplifiers, and have spent the last five years developing a SE amplifier. I was lucky to buy two pairs of VV32B tubes (big uncle to 300Bs)
I wound prototype OPTS with split-bobbin windings and the usual silicon-steel laminations - an "ancient" winder had instructed me to stick with them.......
Closely read the Thorsten description of the We91 circuit using a pentode driver, and substituted a C3G mu-follower driver circuit - despite Thorsten's hesitance towards it. I had more HT available and the first result was to pop my scope (Techtronics) with an excess output ~ 200v.
Trustingly, I built a filament DC supply for the output-triode. Thorsten achieved ~ 18mv ripple - I achieved ~ 3mv. I used a typical pye filter with lots of C before and after an iron-cored choke. I also included a ~ 30mm diameter toroidal choke wound common-mode right at the output-tube socket. I have not included caps here.
I invited my partner to place her ear within the bare 12" driver and listen. She says "Turn it on - can't hear nothiing". I say, "It is on!!!!"
Sadly, the noise-floor enjoyed on both mono-blocks is compromised when connected to the pre-amp...working... working.
My Statement: DHT triodes can operate completely noise-free with a DC supply.....fabulously at the moment ......and about to get better....
Graeme
I have run Audio Research D76 clones for many years - quiet insofar as base noise levels go - lovely - but the GEC KT88s have aged like me and I do not have a closet-full of replacements... I succombed to the hoopla of SE amplifiers, and have spent the last five years developing a SE amplifier. I was lucky to buy two pairs of VV32B tubes (big uncle to 300Bs)
I wound prototype OPTS with split-bobbin windings and the usual silicon-steel laminations - an "ancient" winder had instructed me to stick with them.......
Closely read the Thorsten description of the We91 circuit using a pentode driver, and substituted a C3G mu-follower driver circuit - despite Thorsten's hesitance towards it. I had more HT available and the first result was to pop my scope (Techtronics) with an excess output ~ 200v.
Trustingly, I built a filament DC supply for the output-triode. Thorsten achieved ~ 18mv ripple - I achieved ~ 3mv. I used a typical pye filter with lots of C before and after an iron-cored choke. I also included a ~ 30mm diameter toroidal choke wound common-mode right at the output-tube socket. I have not included caps here.
I invited my partner to place her ear within the bare 12" driver and listen. She says "Turn it on - can't hear nothiing". I say, "It is on!!!!"
Sadly, the noise-floor enjoyed on both mono-blocks is compromised when connected to the pre-amp...working... working.
My Statement: DHT triodes can operate completely noise-free with a DC supply.....fabulously at the moment ......and about to get better....
Graeme
DHT O/P TUBES
Graeme,
Interesting Comments regarding the 300B vs KT88 argument. Are you aware of the Audion Silver Night 300B Amps.
They are the only commercially made amps I have worked on using DHT, there may well be others. The filtering in the filament supplies is purely RC, so the noise floor on them, already very low, could no doubt be reduced even further with chokes(no space on the chassis, though!
Graeme,
Interesting Comments regarding the 300B vs KT88 argument. Are you aware of the Audion Silver Night 300B Amps.
They are the only commercially made amps I have worked on using DHT, there may well be others. The filtering in the filament supplies is purely RC, so the noise floor on them, already very low, could no doubt be reduced even further with chokes(no space on the chassis, though!
Bottlehead Amplifiers
Can't say I've ever heard of Bottlehead Amplifiers. Maybe they're not known in the UK? Are they HiFi, PA, or Guitar Amps? Out of curiosity do you have a schematic. Might be useful one day?
Time permitting, I will either post the schematic for the Audion Amp, or the website address from where I obtained it, since it may be of use to other forum members
Can't say I've ever heard of Bottlehead Amplifiers. Maybe they're not known in the UK? Are they HiFi, PA, or Guitar Amps? Out of curiosity do you have a schematic. Might be useful one day?
Time permitting, I will either post the schematic for the Audion Amp, or the website address from where I obtained it, since it may be of use to other forum members
Hi,
Thanks for the interest....
The amplifiers were constructed on wooden plinths with a brass top-plate. A central rib separates the power-supply from the amplifier stages. Factors which may have contributed to my success are:
A small encapsulated mains filter.
The power transformer was wound with a copper-shim shield over the primary winding. The HT centre-tapped secondary was wound "inside-out". From the core the first half starts as the CT and finishes as HT. Substantial insulation here. The second half starts as the HT and finishes as the CT. The two outers are joined tgogether. I balance the DC resistance with a small resistor in series with the low side. Rectifiers are 6CJ3 damper-tubes and achieve 500v at the cathodes.
The HT filtering is CLCRC - namely 6mfd prop/foil input, a substantial choke measuring 168ohms DC, 100mfd ASC cap, 200ohm resistor, 100mfd ASC cap. Included is a 15mfd prop cap from HT to the output=tube cathode.
A central star-earth point is rigidly followed - every-return terminates here.
The driver is the typical mu-follower circuit using C3gs and ~ 430v HT. Lower cathode is by-passed with 47mfd Obligato. The VV32Bs are run at 396v across and 90v cathode-bias - around 95ma.
The driver tubes enjoy a separate filament transformer - copper-shim included. The two windings are centre-tapped and are lifted to 40v and 240v following Morgan Jones' Thingy.
The DC filament supply starts with ~ 8vAC under load. Bridged-rectified with discreet Schotky diodes by-passed with RIFA 4700pfd. Pi-filter starts with 10,000mfd, iron-core choke (136 turns of 0.9mm) and 15,00mfd. The toroid at the tube-socket is wound in common-mode on a 40mm yellow/white toroid.
Hopefully - with much needed assistance - I can share a photo or two......
Graeme
Thanks for the interest....
The amplifiers were constructed on wooden plinths with a brass top-plate. A central rib separates the power-supply from the amplifier stages. Factors which may have contributed to my success are:
A small encapsulated mains filter.
The power transformer was wound with a copper-shim shield over the primary winding. The HT centre-tapped secondary was wound "inside-out". From the core the first half starts as the CT and finishes as HT. Substantial insulation here. The second half starts as the HT and finishes as the CT. The two outers are joined tgogether. I balance the DC resistance with a small resistor in series with the low side. Rectifiers are 6CJ3 damper-tubes and achieve 500v at the cathodes.
The HT filtering is CLCRC - namely 6mfd prop/foil input, a substantial choke measuring 168ohms DC, 100mfd ASC cap, 200ohm resistor, 100mfd ASC cap. Included is a 15mfd prop cap from HT to the output=tube cathode.
A central star-earth point is rigidly followed - every-return terminates here.
The driver is the typical mu-follower circuit using C3gs and ~ 430v HT. Lower cathode is by-passed with 47mfd Obligato. The VV32Bs are run at 396v across and 90v cathode-bias - around 95ma.
The driver tubes enjoy a separate filament transformer - copper-shim included. The two windings are centre-tapped and are lifted to 40v and 240v following Morgan Jones' Thingy.
The DC filament supply starts with ~ 8vAC under load. Bridged-rectified with discreet Schotky diodes by-passed with RIFA 4700pfd. Pi-filter starts with 10,000mfd, iron-core choke (136 turns of 0.9mm) and 15,00mfd. The toroid at the tube-socket is wound in common-mode on a 40mm yellow/white toroid.
Hopefully - with much needed assistance - I can share a photo or two......
Graeme
Re: Bottlehead Amplifiers
US based supplier of relatively affordable hi-fi kit amps and pre-amps:
Bottlehead
You may not want to open the site at work, if your employers would not appreciate the nicely photographed (and quite undressed) model in their product photographs.
OXAUDIO said:
US based supplier of relatively affordable hi-fi kit amps and pre-amps:
Bottlehead
You may not want to open the site at work, if your employers would not appreciate the nicely photographed (and quite undressed) model in their product photographs.
DHT Audio Amplifier
The attached thumbnails are pictures of the amplifier constructed by Graeme(see post 69), who has asked for assistance with posting them on this forum
(PS- I thought I was attaching THREE Thumbnail images, which can be enlarged by the viewer. Obviously not, so how do you do this?!)
The attached thumbnails are pictures of the amplifier constructed by Graeme(see post 69), who has asked for assistance with posting them on this forum
(PS- I thought I was attaching THREE Thumbnail images, which can be enlarged by the viewer. Obviously not, so how do you do this?!)
Attachments
Re: Re: Bottlehead Amplifiers
dont want to start WWIII Johan as I comletely agree with you,v DHT / DHF is a compromise and I believe you are saying has to be tackled in a sound way. however, having spent the last week having ground this out I think I see why these tubes are not a disaster...
Mu
low gain tubes! if yr gain is only 3 or 4 then any ripple at the cathode isn't exactly amplified: please consider voltages = 40v Pk -Pk vs a few mv rippple.
It actually hurt to admit that (oww..) But is that faulty logic, anyone?
Hmmm frankly If youre an engineer and your employer objects to the bottlehead site, probably time to look for another job anyway.. Face it chaps engineers are NOT on the ascendency where you come from
Andy - currently developing a virtual mirror for the view from below the 300b
Johan Potgieter said:
dont want to start WWIII Johan as I comletely agree with you,v DHT / DHF is a compromise and I believe you are saying has to be tackled in a sound way. however, having spent the last week having ground this out I think I see why these tubes are not a disaster...
Mu
low gain tubes! if yr gain is only 3 or 4 then any ripple at the cathode isn't exactly amplified: please consider voltages = 40v Pk -Pk vs a few mv rippple.
It actually hurt to admit that (oww..) But is that faulty logic, anyone?
lousymusician said:
Hmmm frankly If youre an engineer and your employer objects to the bottlehead site, probably time to look for another job anyway.. Face it chaps engineers are NOT on the ascendency where you come from
Andy - currently developing a virtual mirror for the view from below the 300b
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