Can someone please measure the total height from chassis to the top of the tallest valve? My estimation is that, if chassis is 3" tall, the distance from chassis to the top of the tallest valve should be around 4". An estimation made only by looking at the assembly pictures.
May someone put a rule for a second and give me a hand?
The height measurement for the completed amp is 8.5" from the table top to the top of the KT88s. If I remember correctly, I rounded off that measurement a little long. That is with the wood side panels and little rubber feet that come with the panels. The photo of the perforated cover certainly "looks" taller than 5.22" indicated on the engineering drawing. I'll take another accurate measurement when I'm at the office tomorrow and let you know.
Concerning exposed high-voltage. There are no exposed high voltages present on this amplifier. Yes, the tubes do get hot. That would be a concern if you have little folks around that might be tempted to touch the "pretty lights".
Scott
Not sure if you have materials available to make your own, or if you have tools available to fabricate something like a "bird cage", but here are a few ideas.
Here's a link to some decorative screen or mesh materials.
China Perforated Metals (Hole Shape) manufacturer & supplier - Anping Yilida Metal Mesh Co., Ltd.
My local hardware store stocks a few different styles to pick from. I've been thinking of making a cover out of it, mainly for aesthetics -- but also for the possible little ones who need to touch things that might be hot. I live alone and don't get many visitors, so it's been low on the priorities so far.
Here's a link to some decorative screen or mesh materials.
China Perforated Metals (Hole Shape) manufacturer & supplier - Anping Yilida Metal Mesh Co., Ltd.
My local hardware store stocks a few different styles to pick from. I've been thinking of making a cover out of it, mainly for aesthetics -- but also for the possible little ones who need to touch things that might be hot. I live alone and don't get many visitors, so it's been low on the priorities so far.
I'm not sure that the Hammond offering could be modified to work with the side panels due to the the bracing details shown in the engineering drawings. Maybe. I will check the actual height as I said earlier, in case you don't want to use the side panels.
I agree with Dave, your local "home store" may offer solutions similar to the link provided by Dave. A little fabrication could yield a good alternative.
All of my tube amps are at my work location. I work with fine folks, but sometimes you've just got to wonder what might happen next.
Scott
I agree with Dave, your local "home store" may offer solutions similar to the link provided by Dave. A little fabrication could yield a good alternative.
All of my tube amps are at my work location. I work with fine folks, but sometimes you've just got to wonder what might happen next.
Scott
I have already checked the measures and it is feasible to flip the lateral sides 90º degrees so to be horizontally screwed to the wood. I have made my calculations with Hammond datasheets and it seems to fit. Now I have to think a proper way to flip 90º the 9.53mm steel flap, in a not-very-messy way.
Hammond Mfg. - Perforated Chassis Covers (1451 Series)
P/N:1451-30
Another consideration is cost, Farnell charges me around 75€ plus delivery for this part.
Yeah, by exposed I mean a "meaningful risk of beating a valve, breaking the glass, thus touching the cathode".
My approach use to be to always think of the worst case scenario. I don't have small childs around home, but I consider myself enought messy to have an accident.All of my tube amps are at my work location. I work with fine folks, but sometimes you've just got to wonder what might happen next.
I am confident enoght to beat, kick and throw away to the floor my SS designs, and be sure that, not only I will not get a shock, but they will be in a 100% operational state (ok, maybe external connectors may suffer damage).
From tabletop to the top surface of the chassis is 3.25".
From the top surface of the chassis to the top of the KT88 (highest point) is 4.25".
I just ordered the master kit, and am very much looking forward to building the amp.
A quick question. Has anyone tried using LEDs to bias the 6N1P. I would think a couple of red LEDs should work, like the HLMP-6000.
Be interested in hearing anyone thoughts or results if they tried it.
Debra
A quick question. Has anyone tried using LEDs to bias the 6N1P. I would think a couple of red LEDs should work, like the HLMP-6000.
Be interested in hearing anyone thoughts or results if they tried it.
Debra
The HLMP-6000 have a Vf of 1.6V so two of them will give a 3.2V bias.
There are a couple of others in the HLMP-6xxx series that could work.
HLMP-6400 have a Vf of 2.0V these are yellow LEDs
HLMP-6820 have a Vf of 2.1V these are green LEDs
I just happen to have a number of the red HLMP-6000 from other projects lying around.
The max forward current is lower for these HLMP-6400 20ma and the HLMP-6820 30ma (the HLMP-6000 is rated at 50ma).
I think either of these will still have enough safety margin?
Let me know if my thinking is correct
Debra
There are a couple of others in the HLMP-6xxx series that could work.
HLMP-6400 have a Vf of 2.0V these are yellow LEDs
HLMP-6820 have a Vf of 2.1V these are green LEDs
I just happen to have a number of the red HLMP-6000 from other projects lying around.
The max forward current is lower for these HLMP-6400 20ma and the HLMP-6820 30ma (the HLMP-6000 is rated at 50ma).
I think either of these will still have enough safety margin?
Let me know if my thinking is correct
Debra
Just trying to see if I understand this correctly.
If I were to bias the 6n1p with two HLMP-6000, the new bias voltage would be about 3.2V. This would give a slightly higher Plate current. In the original design the current is 4mA, an easy point to read off the curves. Changing to the 3.2mA bias the current would increase to around 5mA if I extrapolated the curves correctly (eyeballing on the computer screen). Would you have to decrease the Plate resistor to keep the plate voltage constant and keep you out of a nonlinear part of the curve. If the 3.2V bias truly gives around a 5mA bias current than the by my calculations the plate resistor should be dropped to around 39K to put you on a linear part of the curve.
I may be way off here, but trying to understand how the circuit works.
Debra
If I were to bias the 6n1p with two HLMP-6000, the new bias voltage would be about 3.2V. This would give a slightly higher Plate current. In the original design the current is 4mA, an easy point to read off the curves. Changing to the 3.2mA bias the current would increase to around 5mA if I extrapolated the curves correctly (eyeballing on the computer screen). Would you have to decrease the Plate resistor to keep the plate voltage constant and keep you out of a nonlinear part of the curve. If the 3.2V bias truly gives around a 5mA bias current than the by my calculations the plate resistor should be dropped to around 39K to put you on a linear part of the curve.
I may be way off here, but trying to understand how the circuit works.
Debra
That looks to be about right. I've read that when biasing with LEDs, a little more current, say around 10mA, helps with the linearity. With this circuit, the current through the 6N1P could be increased to 6mA by paralleling a 68K 2W resistor with the existing 47K. That would be an effective 28K (about), and would also maintain the -4V bias point. At 6mA, if you wanted to go back to a resistor/cap for the bias, the new value is 680R 1/2W.
Just out of curiosity, is it possible to get the part numbers of the MP oil capacitors?
ASC Capacitors - Products
ASC Capacitors - Products
One more LED bias question. I have done some reading on this circuit. Some are advocating biasing the 6N1P at around 3.2V or so (two 1.6V red LEDs) , instead of the 4V the specified resistor will give you. This bias point should run the tube at a slightly higher current. If you were to do this does the 47K plate load resistor need to be tweaked?
Also has anyone tried replacing the plate load resistor with a constant current source?
Debra
Also has anyone tried replacing the plate load resistor with a constant current source?
Debra
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.