Hi,
I have a pair of output transformers, Hashimoto - HW-100-5, PP 100w RMS/30Hz. I plan on doing two monoblocks using the circuit below. Somebody has already built this amp? For this pair of transformer, is there any other circuit to be recommended?
Thanks in advance.
http://www.tube-amps.net/images/KT88_PP_01/KT88_Schematic.jpg
I have a pair of output transformers, Hashimoto - HW-100-5, PP 100w RMS/30Hz. I plan on doing two monoblocks using the circuit below. Somebody has already built this amp? For this pair of transformer, is there any other circuit to be recommended?
Thanks in advance.
http://www.tube-amps.net/images/KT88_PP_01/KT88_Schematic.jpg
For the anode HT output, assume a full wave bridge rectifier is being used to get the 525 volts. Also, the high heater to cathode voltage on the driver 12AU7 is of concern....hopefully the heater winding is "floating" or biased to some positive voltage to keep the max heater/cathode voltage within spec....
Why don't change the EF86 in pentode to connecting as triode, will have better curves and enough gain, Maybe can reduce the NFB to a few db.
I like the bias pot balance of this schematic to match the two half waves. but how can you check that the match is correct ?
One friend told me if put to iron pin on the OPT when you can not feel any magnet field half waves are matched, but is possible to check without oscilloscope?
I like the bias pot balance of this schematic to match the two half waves. but how can you check that the match is correct ?
One friend told me if put to iron pin on the OPT when you can not feel any magnet field half waves are matched, but is possible to check without oscilloscope?
I also have a pair laying down in the office.
My thinking:
1 use ready to use board like peter millet uniamp and drive it to the max, maybe 40W?
2 schematics like oddwatt does not impress me with one stage driver
3 schematics from the package is nicer, but why build an pp amp with single ended input? Why just do balanced input, ultralinear, two stage driver (i prefer 6sn7 lines), and operate it near the maximum power output?
My thinking:
1 use ready to use board like peter millet uniamp and drive it to the max, maybe 40W?
2 schematics like oddwatt does not impress me with one stage driver
3 schematics from the package is nicer, but why build an pp amp with single ended input? Why just do balanced input, ultralinear, two stage driver (i prefer 6sn7 lines), and operate it near the maximum power output?
Re: Default OT PP Hashimoto HW-100-5 tube amp?
The reason I was particularly drawn to this Hashimoto design was that I was looking for one that implemented the ideas set out in the article (link below) for a 100 watt output Push-Pull KT88 design based on the classic Williamson Amplifier design:
Valve Amps: Valve Amps
The Lenard Audio pages are a fantastic read, especially where he explains why you really need 100w capacity to give you enough headroom for true 'high fidelity' reproduction. This was one of the few designs where I'd seen the KT88's pushed to 560V HT on the output transformer (which that can take comfortably) to give 100w.
I like the Pete Millett design too, especially his PCB for the driver section (though it uses a different phase inverter and input transformers) but I've heard conflicting reports on how high the output can pushed. Interested to hear all your views?
The reason I was particularly drawn to this Hashimoto design was that I was looking for one that implemented the ideas set out in the article (link below) for a 100 watt output Push-Pull KT88 design based on the classic Williamson Amplifier design:
Valve Amps: Valve Amps
The Lenard Audio pages are a fantastic read, especially where he explains why you really need 100w capacity to give you enough headroom for true 'high fidelity' reproduction. This was one of the few designs where I'd seen the KT88's pushed to 560V HT on the output transformer (which that can take comfortably) to give 100w.
I like the Pete Millett design too, especially his PCB for the driver section (though it uses a different phase inverter and input transformers) but I've heard conflicting reports on how high the output can pushed. Interested to hear all your views?
between katodes pin 8 of KT88 should measure ZERO 0mV DC at idle but the sense resistor should be 10ohm matcheds perfectly, so TP for each KT88. (some KT 88 have metal base connected to kathode , but not JJ KT88, easy TP all ready available in commercial amps)
first between grd and TP pin 8 you check global bias and then fine tune balance bias between TP , everytime this test should be made to check pp stage
Last edited:
The everyday output power from my amp barely exceeds 1W out of 60 nominal RMS, with rare peaks at 5W, yet it sounds quite loud. I can feed my speakers with 100W and even more, but that will turn me deaf and neighbours furious.
BTW, I have built and tuned Williamson, it works, IMHO its not the best circuit around, takes time to get it stable, relatively high level of 3rd and 5th harmonics. There are much better circuits published on this forum based on Mullard 520.
Hi,
New member and I just can't resist to post here.
The schematic at the entry post is exactly what I built some eight years ago only with
different OTPs and chokes. In fact, this was my first ever attempt to tubes world and
I was attracted by simplicity. I found out that this is a design to move rather inefficient
speakers, not my preference. Over the years I modified it extensively, learning everything I know about tubes. The most important issues of this design are in the phase splitter
having the same psu rail with the power tubes and of course exceeding nominal cathode to heater voltage. Below are the current status schematics
Unbalanced class AB version
Unbalanded class A version
Balanced class A version
New member and I just can't resist to post here.
The schematic at the entry post is exactly what I built some eight years ago only with
different OTPs and chokes. In fact, this was my first ever attempt to tubes world and
I was attracted by simplicity. I found out that this is a design to move rather inefficient
speakers, not my preference. Over the years I modified it extensively, learning everything I know about tubes. The most important issues of this design are in the phase splitter
having the same psu rail with the power tubes and of course exceeding nominal cathode to heater voltage. Below are the current status schematics
Unbalanced class AB version
Unbalanded class A version
Balanced class A version
Attachments
Last edited:
Nice work though.
I am reading Lenard articles about new schematics for modern amps and Opens my mind not to stick on old school circuit building. Articles about negative feed back, bootstrap mechanism, opamp as preamp driver and power supply regulations are things we really have to consider to imolement in our design.
I am reading Lenard articles about new schematics for modern amps and Opens my mind not to stick on old school circuit building. Articles about negative feed back, bootstrap mechanism, opamp as preamp driver and power supply regulations are things we really have to consider to imolement in our design.
If you had built one you might change your tune. Sonic signature of a SE with the power of a PP - whats not to like.
Shoog
Thanks for the reply - Interesting to hear your thoughts on the stability issues. Will check out the Mullard 520 designs you mentioned. Do you have any links handy that I could check out to save time searching?
As for the power output I'm looking for, it's not about a search for loudness as such and I do appreciate how and why tube amps can sound comparatively louder per watt output than solid state - there are some interesting insights into how and why the differences arise between the two on the same site I mentioned - see the voltage drive v's current drive comparison at Amplifiers: Solid State amps verses Valve amps
The reason why I was looking for a tube design to give me UP TO 100 watts output, was really about getting the full dynamic range available from music without it going into clipping (even if tubes clip softer) - have a look at this also from the same site: Amplifiers: Output stage, in particular under the heading RMS Power and Music Compression where it explains:
"Music is capable of a 60dB (1,000,000:1) dynamic range. The transients in music are very small in energy but are approx 20dB above the RMS music level. The average RMS power of fully dynamic music can not go above -20dB of the amplifiers full power capacity without the transients clipping the rail supplies. 20dB is 100:1 so therefore a 100 Watt amplifier should not be driven above 1 Watt of RMS music level (over approx 1 minute of time) to avoid transients being driven into rail clipping. A 100 Watt amplifier can only be used at an average of 1 Watt with fully dynamic music. For this reason amplifiers less than 60 Watts should not be considered as audiophile status, but unfortunately many are."
lemondixon people are happy by 8w 300B from 60year maybe ?
you don't need 100w ,only if ss and 10db in real life
all class A Pass amp are only 25w ss go figure ! F6- M2 F7 Sit1
you don't need 100w ,only if ss and 10db in real life
all class A Pass amp are only 25w ss go figure ! F6- M2 F7 Sit1
Well you're absolutely right in that everyone is entitled to their own opinion, and you don't feel that you need 100 watts output, but I wasn't asking for validation of the idea - only if anyone knew of designs to achieve this end and, if so, how they worked out.
Just because people have been happy with something for a long time doesn't mean there's no good reason to try to improve on it. I have a single ended hifi tube amp and really love the sound, as I also love the sound of my guitar tube pre-amp, yet I still have various solid state amps - some are amazing, and some nothing special. None the less, I still want to experiment with the best that tube amps have to offer (and appreciate that 'best' is completely subjective - so let's not get into that)
However, if it hadn't been for transistors killing off the mainstream tube amp market and so investment in continuing development, there clearly would have been a lot of important improvements to what people now consider to be the best you can get from a tube amp. By the late 1950's singled ended was pretty much universally considered 'inferior' (by designers of the time) to the performance to be obtained from push pull if you look at the writings of the experts at the time and where developments were headed. Just look at the GEC designs catalogue - http://www.tubebooks.org/Books/GEC_approach.pdf
or the writings of Crowhurst for example - http://www.tubebooks.org/Books/Atwood/Crowhurst%20Cooper%201956%20High%20Fidelity%20Circuit%20Design.pdf
Having said that, it seems that if you want the sound of single ended, but with the extra power and headroom to give you a full dynamic range then there are 100 watt designs now being produced as 'double parallel single-ended' such as this by Unison Research: Reference - Unison Research - Official Website
So you see, not 'everyone' is 'happy' with 8 watts from 300B, nor does tube amp technology (and our expectations) have to remain static!
These mono-blocks by Unison Research look amazing and I would be very interested to hear from anyone who knows the details of such a circuit design and their experience of them. I will be going to audition a pair of these amps soon out of curiosity.
Attachments
this can help you http://www.diyaudio.com/forums/tube...-crisis-my-833c-amp-build-12.html#post3773197 
my carver silver seven 600w can put out 1200w on 2ohm I feel no problem with 300b ...
my carver silver seven 600w can put out 1200w on 2ohm I feel no problem with 300b ...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.