Moderator: kabubi
kabubi wrote:you just gotta watch out for the microphonics of the tube, sir. the 26 can howl, hiss, crackle and grate. but like a wild, strong stallion, it can be tamed.
the Master at Calatagan (soon to be recognized as the Master of Matanzas once again) found a way to tame the microphonics, and i think it had got something to do with the casing/chassis.
good luck on your endure. as they say, "Nothing ventured, nothing gained."
AbadSantos 7 wrote:Everyone says Life Begins at 40. For every one of us its really 40s… is the starting point in life that the next we need to think is
retirement in future. I won’t argue with others that life begins even earlier with this mentioned age .
Anyway, Im 40 and yes Im thinking of the future which include my audio journey.
Pardon my English and grammar since Im not a good writer , just writing this to document my DIY adventure which
will include excitement, failure, frustration, funds limitation, and many others obstacle I can encounter in building this project of mine.
I will not cheat on each detail, from the parts preparation, time line (since funds are the main limitation expect a very long time line),
assembly (what problem and obstacle I can encounter) and of course the end result will be in real time. Pass or fail will be documented
or even my mood to stop or continue once I decided DIY is not for me.
Im not good in describing sound but I know what my objective is….
The main problem now I’m seeing is aside from funds is I DON'T HAVE THE DIY SKILLS.
(Disclaimer: I’m including some technical write-up based on my personal interpretation of the schematic diagram or any hazard
voltage information available on each test point. These are only my personal analysis and no way can it be used as official information.
There is high chance of mistake on my part thus, resulting to high risk.
This journey is not also to encourage others to go to DIY simple because of the Dangerous High Voltage that can cause risk to your life).
26 DHT Pre-Amp
I was captivated by 26DHT Pre-amp in its characteristics. Honestly, I didn't hear it yet. Based on several forums, they can promise what this
pre-amp can deliver. Some said this is very truthful to music, others say its just a straight forward pre-amp. If you feed junk, it will give you junk.
If you can tweak, they swear can give you the most honest sound that other pre-amp cannot give. In other words, this is one of the ultimate pre-amp
out there to its existence.
As old designers saying, Design still the key point. Kevin Kennedy’s 26DHT Pre-amp capture my attention which they say one of the most good
design for this kind of pre-amp. In-fact, no other than the Master in Calatagan St. Lungsod ng Makati has built several of this unit.
viewtopic.php?f=36&t=8384&start=360
Start of the DIY Journey…
BOM Preparation:
Starting with Capacitors:
1.0 C1/C2 – 0.1uf/400V TFT
2.0 C3/C4 – 0.47uf/100V Film
3.0 C6 – 8200uf/10V
4.0 C7 – 100uf/16V
5.0 C8 – 47uf/450V min
6.0 C9 – 68uf/450V min
7.0 C10 – 1.0uf/200V Film
8.0 C11 – 2.2uf/400V Film
9.0 C12 – 22uf/630V Film
I will focus first on power Supply:
Based on Power transformer requirement, it will require a minimum of 600V to 700V CT feeding a 5AR4 rectifier tube. Its my understanding
before on my ELCE 313/ELCE 311L and EECE 313/EECE 311L that it will have 300V to 350V rail voltage for the tube output line.
Schematic as follows (broken)
PT (600~700V CT) 5AR4 C8 Resistor C9 ………….next stage to EL84…
So the C8 and the C9 are the first line of defence in filtering the input signal coming from AC outlet... converted to DC?
Presuming a 350V rail voltage, my assumption will have at least 500 to 525V at this check point.
So my requirement for my capacitor (C8) voltage capability will range from 625 to 656V. Based on current list of MKP capacitor...
the most suitable will be 630V.
So my C8 will be 47uf/630V.
Since a resistor is connected to reduce the next stage rail voltage for EL84, my assumption will not deep dive for a much significant
voltage drop(since EL84 Screen voltage is about 300V) since based from BOM still need to carry at 450V min requirement. So its safe to
stay at 630V range since the next MKP type will be at 400V. Very danger to go down to 400V i think.
So C9 will be at 68uf/630V.
This now the problem occurs. 68uf/630V is not readily available at least to some known capacitor in the market today.
My solution is 47 + 10 + 10 + 1 / 630V connected in parallel. Is my math ok? Now will check how much this will cost me.
Oh my…..MKP capacitor is not cheap…. when you are talking about non-branded to branded type of capacitors nor compare to electrolytic
type. Since this pre-amplifier will be truthful.. I don't like compromise to feed with non-trusted brand nor a el cheapo since Im afraid I
cannot obtain my objective at the very least.
Huhuhu wo de zi jin mei you le…
Mundorf don't have this type of value..so I will settle at least for the SCR MKP type capacitor. Which have 47uf, 10uf, and 1uf/630V
are readily available.
So I ordered and waiting what will be the exact appearance.
So next time as I go along with this project.
kabubi wrote:you just gotta watch out for the microphonics of the tube, sir. the 26 can howl, hiss, crackle and grate. but like a wild, strong stallion, it can be tamed.
the Master at Calatagan (soon to be recognized as the Master of Matanzas once again) found a way to tame the microphonics, and i think it had got something to do with the casing/chassis.
good luck on your endure. as they say, "Nothing ventured, nothing gained."
hypertriode wrote:kabubi wrote:you just gotta watch out for the microphonics of the tube, sir. the 26 can howl, hiss, crackle and grate. but like a wild, strong stallion, it can be tamed.
the Master at Calatagan (soon to be recognized as the Master of Matanzas once again) found a way to tame the microphonics, and i think it had got something to do with the casing/chassis.
good luck on your endure. as they say, "Nothing ventured, nothing gained."
Kabubs & Loi, you have to talk to BenC as he has licked the hum problems of the 26 without the mumbo-jumbo!
tony wrote:your raw dc after the 5AR4 will be around 420 to 490 volts dc, that is why capacitors are speced at 630volt, 400volts will not work here....the 5AR4 really likes 40ufd right after its filament, Kenedy chose 47ufd which is still okey, although you can use 22ufd or even 39ufd/630volts, these are standard values....for the next capacitor, you can use 2 x 39ufd caps....http://www.positive-feedback.com/Issue16/kennedy.htm
Design Considerations
Being originally somewhat budget-minded orientation on this project, I choose to use as many junk box components as I could muster. A surplus encapsulated supply was used to provide both bias and filament power. Any supply that can provide at least 2 - 3A @ 5.0V and -12V or -15V @ 100mA will serve nicely. For those who are more ambitious or just don't have the requisite supply in their junk box, several other options will be mentioned below.
kabubi wrote:"Nothing ventured, nothing gained."
tony wrote:you may be surprised to find out that dealing with tubes, unloaded rails drops bigtime when loaded, that is why for an amp with rails of 150volts had to resort to such psu topology....you may also look at the Salas series-shunt regs which has been validated as being very potent.....
the 6BQ5 cum 12AX7 regulator is just another amplifier within your preamp...so in effect you are building 2 amps in one project......there are other ways of powering up your preamp....
this preamp is a bit complicated for an upstart, look at broskie's blogs and you will find a lot of ideas/projects.......with pcb's so that building by newbies assures success...
from the kennedy blog, i used to exchange emails with this guy, he is very accommodating........Design Considerations
Being originally somewhat budget-minded orientation on this project, I choose to use as many junk box components as I could muster. A surplus encapsulated supply was used to provide both bias and filament power. Any supply that can provide at least 2 - 3A @ 5.0V and -12V or -15V @ 100mA will serve nicely. For those who are more ambitious or just don't have the requisite supply in their junk box, several other options will be mentioned below.
tony wrote:you may be surprised to find out that dealing with tubes, unloaded rails drops bigtime when loaded, that is why for an amp with rails of 150volts had to resort to such psu topology....you may also look at the Salas series-shunt regs which has been validated as being very potent.....
the 6BQ5 cum 12AX7 regulator is just another amplifier within your preamp...so in effect you are building 2 amps in one project......there are other ways of powering up your preamp....
this preamp is a bit complicated for a newbie, look at broskie's blogs and you will find a lot of ideas/projects.......with pcb's so that building by newbies assures success...
from the kennedy blog, i used to exchange emails with this guy, he is very accommodating........Design Considerations
Being originally somewhat budget-minded orientation on this project, I choose to use as many junk box components as I could muster. A surplus encapsulated supply was used to provide both bias and filament power. Any supply that can provide at least 2 - 3A @ 5.0V and -12V or -15V @ 100mA will serve nicely. For those who are more ambitious or just don't have the requisite supply in their junk box, several other options will be mentioned below.
endrik35 wrote:I agree with you on the salas shunt reg Tony! Made my diy pass B1 preamp a dream! Even the dual rail salas shunt psu built by my friend Leslie brings wonders to my phonostage! More power Loi and happy building!:-)
tony wrote:i buy sockets and stuff out of Zhenzen in China, you should have no problem sourcing parts.....my first advice is do not be bogged down by capacitors, they are aplenty where you are....motor run caps also bring excellent results, you can ask edrel and alexg.... a motor run cap rated for 440volts ac works perfectly for 600 volt dc rails....
alexg wrote:[quote="AbadSantos 7"
So if I see an AC cap with lower working voltage, what will be the factor for to work safely to DC? Or not all will work for DC?
camotecue wrote:Sir,
You can also ask for some tips from oca imperio (oscarmiguel of ws). He has been successful in his designs for the 26 DHT - may it be in his preamp design or in his DHT amp designs with 26 as driver tube. He lately utilizes DHTs in all his amps/preamps and no IDHTs as driver tubes anymore. No noticeable hum whatsoever in his horn speakers. I myself is using a 26 driven 2a3 SET amp designed by Oca. I'm using horn speakers also.
I think andyjevans of diyaudio has also a successful implementation of the 26 preamp.
If not done properly, the 26 DHT is notorious for hum.
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