One other important fact that I did not intend to be remiss in reporting:
If you're providing your own transformers, please pay attention to the transformer specifications as shown on the Master Kit transformer list.
Scott
If you are providing your own chassis, the hardware included in the Basic Kit will work with chassis top plate thickness of up to 0.125".
According to the rules of this site, this thread can remain open for technical discussion, so I welcome any questions or comments regarding the technical aspects of this amplifier. Especially since the Vendor's Forum post seems to be such a dismal failure.
Scott
Scott
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Scott,
Just a suggestion, but you might want to put a link to your Vendor Forum thread in your signature line.
I am still interested in a Master Kit, so consider 1 of the 25 sold. If you want to tell me the shipping charges to 66219, we can get that taken care of 😀.
Bill
Sounds great, thanks for the idea Bill. I will respond to you via PM with the shipping charges.
I'm just trying to follow the rules of this site to the best of my ability, so I'll be here and at the Vendor's forum also.
Presently I own a SE KT88 which runs in triode or pentode mode, it is being used as a no feedback triode amp approx. 5w. also have a tube preamp and a 2a3 PP class A amp.
Never having built a tube amp before I am interested in the Kit because of the 2 stage design and hard wiring, would like to know the nominal primary inductance of the output transformers.
From the info provided it looks that the gap is designed for 120ma?. is this correct.
What substitute driver tube can be used instead of the 6n1pev.
Never having built a tube amp before I am interested in the Kit because of the 2 stage design and hard wiring, would like to know the nominal primary inductance of the output transformers.
From the info provided it looks that the gap is designed for 120ma?. is this correct.
What substitute driver tube can be used instead of the 6n1pev.
The output transformers are gapped for 120mA. I'll have to get back to you with the exact figure, however I believe the nominal primary inductance to be in the 40-50H range.
I have tried the 6N23P-EV for the driver, which is supposedly the equivalent of the 6DJ8/6922/7308, and while it is compatible with the circuit, it just doesn't quite have the "sparkle" of the 6N1P-EV in this particular amplifier circuit, in my opinion.
I picked up my kit at the post office this morning. Everything looks great.
I've got some fabrication to do before I can start assembling, and it will be a few more weeks before I get my transformers, so that's gonna drive me nuts! 😀
Thanks, Scott for making this available to everyone. I'm really looking forward to getting this up and running.
I've got some fabrication to do before I can start assembling, and it will be a few more weeks before I get my transformers, so that's gonna drive me nuts! 😀
Thanks, Scott for making this available to everyone. I'm really looking forward to getting this up and running.
5U4GB minimum limiting resistance
If you are going to build this amp and provide your own power transformer, you must verify that additional resistance is not required between the secondary and the 5U4GB plates. At the B+ voltage of this amplifier, the required limiting resistance for the 5U4GB is about 55 ohms (see the 5U4GB datasheet). The power transformer supplied with the Master Kit meets the requirements and additional resistance is not needed. This webpage discusses how the required value is calculated: The Valve Wizard
See the section of the page called "Minimum Limiting Resistance".
If you are going to build this amp and provide your own power transformer, you must verify that additional resistance is not required between the secondary and the 5U4GB plates. At the B+ voltage of this amplifier, the required limiting resistance for the 5U4GB is about 55 ohms (see the 5U4GB datasheet). The power transformer supplied with the Master Kit meets the requirements and additional resistance is not needed. This webpage discusses how the required value is calculated: The Valve Wizard
See the section of the page called "Minimum Limiting Resistance".
Transformers
Not intending to be an advertisement for Edcor, but the transformer selection listed below makes a good match for this amp if you are providing your own, and the price is right.
EDCOR Electronics Corporation. XPWR010-120/240
EDCOR Electronics Corporation. CXC125-10H-200mA
EDCOR Electronics Corporation. CXSE25-8-5K
I used the power xfmr and choke listed above on the test build, but I used Edcor GXSE for the output. The GXSE are OK, but for a little more money the CXSE will provide much more punch and high-end sparkle.
Scott
Not intending to be an advertisement for Edcor, but the transformer selection listed below makes a good match for this amp if you are providing your own, and the price is right.
EDCOR Electronics Corporation. XPWR010-120/240
EDCOR Electronics Corporation. CXC125-10H-200mA
EDCOR Electronics Corporation. CXSE25-8-5K
I used the power xfmr and choke listed above on the test build, but I used Edcor GXSE for the output. The GXSE are OK, but for a little more money the CXSE will provide much more punch and high-end sparkle.
Scott
Hi Scott,
since the shipping to Europe busts my budget:
Can you just explain (or link me to to an explanation): Why do you use 5k OT's?
All I can get here for an reasenoble price and/or recomended are 2K5 or 3K SE OT's for a SE KT88 Design?
Good Chokes and PT's are available at ease here.
Ciao
Christoph
since the shipping to Europe busts my budget:
Can you just explain (or link me to to an explanation): Why do you use 5k OT's?
All I can get here for an reasenoble price and/or recomended are 2K5 or 3K SE OT's for a SE KT88 Design?
Good Chokes and PT's are available at ease here.
Ciao
Christoph
triode connected ?
funny, but I just read that load of UL tapped is equal or close to triode connected, but I suppose not quite the same 😕
Hi Christoph,
The 5K OT was selected to allow the circuit to run below the maximum dissipation curve with 400V B+, while being biased conservatively at 70mA and keeping unwanted distortion in check. This also allows for this circuit to run the EL34 & 6550 tubes safely. The original Mikael Abdellah design calls for a 5K OT, and many successful builds of this basic design have been constructed based on a 5K OT. If you run a 3K OT in triode mode it will probably be OK until you switch over to the UL tap and then you will be very close, if not beyond the maximum dissipation curve of the KT88. If you can get a 2.5K OT with 4 ohm output you could run 8 ohm speakers and achieve the 5K.
Please someone chime in here if I am way off base.
Check out these links:
Common-cathode triode amplifiers - TuringBirds.com
The Valve Wizard -Single Ended
Scott
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I plotted the load line for 2.5K & 3K for the KT88 biased at 70mA. Operating at 70mA the input would swing way into the knees of the curves. To get the bias point near the center of the load line the tube would have to be biased very close to the max dissipation and then it really doesn't look ideal.
Scott
Thx for the explanation and the discussion.
@Scott: If i would use 4OT's it wouldn't be better for my budget 🙂
Right now, I am in the normal (what I call) "DIY Dilemma": I first have to finish my Loudspeaker (Visaton VOX253), then I have to see if my (heavily pimped) QuadII is able to drive this speaker. If not, I will test an older solidstate project (about 50W), wich never made ist into any housing. If this will also not do it, I will have to build an at least 100W Amp, probably some ClassD stuff. After that, I can think of some 92dB+ horns.
And then there's always this beautiful 300B in my mind.
Since then I have to use my El84 Amp to feed my Stax or my little Horns.
I'm sure that a lot of you guys have similar "problems"
Scott, I sure will keep up track with this amp, I'm still very interested.
Ciao
Christoph
@Scott: If i would use 4OT's it wouldn't be better for my budget 🙂
Right now, I am in the normal (what I call) "DIY Dilemma": I first have to finish my Loudspeaker (Visaton VOX253), then I have to see if my (heavily pimped) QuadII is able to drive this speaker. If not, I will test an older solidstate project (about 50W), wich never made ist into any housing. If this will also not do it, I will have to build an at least 100W Amp, probably some ClassD stuff. After that, I can think of some 92dB+ horns.
And then there's always this beautiful 300B in my mind.
Since then I have to use my El84 Amp to feed my Stax or my little Horns.
I'm sure that a lot of you guys have similar "problems"
Scott, I sure will keep up track with this amp, I'm still very interested.
Ciao
Christoph
Hi Scott,
Could you please confirn the measurement were taken at speaker terminals? What was the load? Purely resistive?
Thanks,
Boky
Could you please confirn the measurement were taken at speaker terminals? What was the load? Purely resistive?
Thanks,
Boky
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