Prototypers wanted

[Fitz]

Okay so quite a bit late to the game (sorry guys ), I'm finally getting all the parts together to get this thing running. Is the CCS tweaking still going on, or is there a general consensus on an updated version I should be using?

[bumpster47]

Hi this is bumpster47. In response to the above message Prototypers Wanted. I have all the skills and tools necessary as well as measuring equipment for this type of assembly. I you would let me know when you need the money the total cost I would be interested and able to participate.

Please e-mail if any questions, [email protected] or [email protected]

[n_maher]

Hi this is bumpster47. In response to the above message Prototypers Wanted. I have all the skills and tools necessary as well as measuring equipment for this type of assembly. I you would let me know when you need the money the total cost I would be interested and able to participate.

Please e-mail if any questions, [email protected] or [email protected]

You have exactly one post left to correct my first impression of you.

[Fitz]

You have exactly one post left to correct my first impression of you.

Nate's being generous tonight.

[n_maher]

Nate's being generous tonight.

He already self-punished by posting his email address, I won't remove that unless asked.

[Pars]

Fitz,

I think the consensus was to stick with the 75 ohm original CCS. Doug threw a wrench in the works (it is his works, so I guess he can do that ) by suggesting another way of getting to the new 2.5-3V grid or cathode bias voltage by using the other CCS (56 ohms, or 221 || 75 ohms) and switching to the resistor grounded cathode jumper setting. See Doug's post 305 for more details. Currently I am playing around with the cathode LEDs (2x red and 1x blue) to try to get in the 2.5-3V range.

[Fitz]

Ok cool, thanks Chris. I got it up and running tonight so I'll listen to it a few days before I start looking at messing around with anything.

[dsavitsk]

Fitz,

I think the consensus was to stick with the 75 ohm original CCS. Doug threw a wrench in the works (it is his works, so I guess he can do that ) by suggesting another way of getting to the new 2.5-3V grid or cathode bias voltage by using the other CCS (56 ohms, or 221 || 75 ohms) and switching to the resistor grounded cathode jumper setting. See Doug's post 305 for more details. Currently I am playing around with the cathode LEDs (2x red and 1x blue) to try to get in the 2.5-3V range.

Actually, I think I'd push the CCS to more like 16-18mA or so, which means a CCS resistor of about 62-56 ohms. Plus, the bias should be over 2V, and closer to 3V if possible. Whether you can do 3.5V bias depends on how loud you listen, and where your tubes bias up.

[Pars]

Listening-wise, I disliked the higher CCS bias, preferring the lower bias by quite a bit. I can perhaps understand the higher bias on Grados... and on rock. Amp is clearer on the lower bias with AKGs.

Here are some measurements of various LED combos on the cathode LED:

2xRed

           L       R

Iled   12.6mA

Vled   3.52Vdc    3.5Vdc

Vplate  181.4Vdc  169.7Vdc


rectangular blue

Iled   12.6mA

Vled   2.98Vdc    2.99Vdc

Vplate  165.5Vdc  154.4Vdc


blue

Iled   12.6mA

Vled   3.0Vdc     3.01Vdc

Vplate  169.1Vdc  156.7Vdc

Edited October 5, 2010 by Pars

[Pars]

Also, can you explain the choice between grounding the output transformers or connecting them to the cathode? I think I have the jumpers correct for the LED on the cathode, but I will need to double check them.

As for your suggestion in post 305 regarding the higher CCS current and using the resistor to ground on the cathode rather than the LED(s), would you also recommend switching the transformer connection in conjunction with this? I'll have to go back thru this thread and the emails to find where you discussed this previously.

[dsavitsk]

Also, can you explain the choice between grounding the output transformers or connecting them to the cathode? I think I have the jumpers correct for the LED on the cathode, but I will need to double check them.

As for your suggestion in post 305 regarding the higher CCS current and using the resistor to ground on the cathode rather than the LED(s), would you also recommend switching the transformer connection in conjunction with this? I'll have to go back thru this thread and the emails to find where you discussed this previously.

An LED on the cathode is, in theory, similar to a resistor bypassed by a capacitor. At a fixed DC (as from a CCS), it drops a fixed voltage, but it acts as a short circuit to AC. Thus, it biases the tube, but does not increase it's impedance. An unbypassed resistor increases the tubes impedance by ~the resistance X mu.

With the LED bias, since there is an AC short to ground, the signal current loop is completed through ground, and thus the transformer primary can be grounded. With the resistor, since there is no capacitor bypass, we need to short circuit the AC somewhere else. Thus, the primary is connected to the cathode which keeps the AC from traversing the resistor, instead being confined to the tube + transformer primary (remember that the plate and cathode are out of phase w/r/t/ each other).

This arrangement seems to work better with high current and a high bias -- i.e., with a large resistor, as this is better able to block the AC. It is kind of like a cathodyne with unbalanced loads, and since the plate Z is so high (nearly infinite) you don't lose amplification even as the bias resistor is increased. With the small bias resistors we started with, I thought is was not great sounding. At higher a higher bias point, i.e., a larger bias resistor, it might be more viable -- I have not tried it yet.

This does raise the question of why not not connect the primary to the cathode with the blue LED that has a pretty high impedance. And, the answer is that it seems to be not high enough and seems to muck with the phase. Try it. I didn't like it.

It also raises the question of why not just use a resistor bypassed by a big cap -- there is some internet lore about how the distortion from electrolytic caps is not measurable, and this turns out to be nonsense. Especially in this spot. The distortion is multiplied by mu, and is clearly higher than the distortion even from a lousy LED.

At any rate, I currently have 66.5R CCS resistors (15mA) and crappy blue LEDs, and it seems to sound pretty good at reasonable listening levels. Problem is that B+ is ~205V and plate voltages are 170V and 180V meaning that I don't have a lot of swing room. But, I can probably increase the power transformer by ~30V which should solve that ... at the cost of some more heat.

[n_maher]

Fabrication continues...

Yesterday was back panel day, I had done all of the layout and marking weeks ago and just hadn't had a big enough window to try to do what I wanted on the mill. This ended up being a blessing since a new vise arrived for the mill in the interim and it's much nicer than the old one. Anyway, my measuring on the RCAs was quite good, although they simply would not fit in a 3/8" hole so I upsized it a 32nd and they fit perfectly, other might want to note that. Also, it would appear that my measuring/layout skills need some work as I definitely oversized the X direction of the IEC a bit. Not horribly, probably .05, but enough to mildly annoy.

Today I somehow managed to find an hour to drill the large holes in the top panel. To give you an idea of the current amount of "tech" being used by the round hole cutter tech here you go. Installed pics will come after I get a few ventilation holes drilled but I tested it and it appears to fit just fine.

This will be the last time that I try to use a large stepped bit. Even with the best work holding tech that $$ can (reasonably) buy and an exceptionally rigid setup it still isn't perfect. The cleaned up holes look pretty good but I think if I'd used a hole saw in this rig I would have gotten better results and obviously a large bit would have been the cat's pjs. I'll definitely be picking up a few large fractional metal bits in the near future.

[Fitz]

Looks good to me, considering I messed up and the IEC hole on mine is oversized by .05-.10 on each side.

[n_maher]

Found another 1/2hr of fab time tonight and got the last of the holes done in the top panel. A few build notes for Tom and Doug - my amp could not be assembled with the bezels in place. If I installed the rear first it pushed the amp too far towards the back and would not allow for proper installation of the front panel. The reverse was also true, front first = can't install back panel, which is to say that the RCAs ended up with inadequate projection. In point of fact even without the bezels it still doesn't all fit perfectly, now the body of the alps is putting stress on the front panel and bowing it out slightly but I think I have a solution for that, details if it works. But enough moaning about the details, what does it look like??!??!

I still have to work out the two standoffs for tube support as well as what I'm gong to use for a knob. I'm also going to do some testing without the top panel heat sink since I provided ventilation for the transformer. I'm hoping it won't require the sink, it'd be a pretty to mess with the general aesthetic.

[Pars]

Looks great Nate! Want to fix my side holes for me? Circle hole cutter tech fail here! Also, do you remember the distances on your tube holes, and how big did you go on these? My brother loaned me a large step bit (looks strangely like the one you picture), that goes up to 1 1/8", but I was thinking about using a 1 1/4" hole saw I have.

Regarding the power transformer, I don't really notice mine getting hot. The heater rectifiers get hot though, and make the front of the transformer hot as well.

[n_maher]

I took the tube hole distances off of Tom's drawings, double checked them and they seemed good so I went with it. They are 1" diameter holes, be very careful if you use a stepped bit that big even in a drill press. Make sure you've got the panel held very securely and run the machine as fast as it'll go or you'll end up with rough edges from the chatter.

And ha, the side holes are a huge pain in the ass. The biggest problem is keeping the extrusion rigid while drilling, I've got some thoughts on how to do it better but it wouldn't be easy.

[swt61]

That looks awesome Nate! The round hole cutter tech has certainly come a long way.

Oh, and I dubb the "Ampicus Phallicus".

[Pars]

Hmm, the only drawings I have are for the end panels. Nothing for the top.

[n_maher]

Hmm, the only drawings I have are for the end panels. Nothing for the top.

I'll try to remember to email it to you tonight or upload it and post a link.

[luvdunhill]

http://www.diyforums.org/Les/construction/templates/TorpedoEndplates.pdf

http://www.diyforums.org/Les/construction/templates/TorpedoTop1.pdf

http://www.diyforums.org/Les/construction/templates/TorpedoTop2.pdf

Note that I put two vertical rows of 1/4" holes ( 8 holes, total) on the side of the case adjacent to the heaters supply heat sink (next to all those 3/16" top holes).

All of the above addresses the heat issues, except that some side holes at the tube positions could help. It depends on how much heat you're willing to accept at the coupling caps, I guess (maybe Doug can add some opinions here). Mine ran without any side holes at the tubes all day, both days at CanJam.

QFT

[Pars]

Thanks!

[HiGHFLYiN9]

Looks awesome Nate I'm really looking forward to this kit whenever it's finalized.

If I handled the fab on this, I'm sure I'd screw up the IEC, then paint the whole thing black so you wouldn't notice

[TomB]

Looks really awesome, Nate! It's great that you'll be testing for the heat around the PT wit those slots, too. I agree that it would be nice to get rid of the heat sink. I tried several dozen smallish holes in the same location as the heat sink, but no bottom or side venting - it didn't work and I put the heat sink back on. We were trying to keep from putting any holes in the bottom of the case and I got fed up with trying to drill through the sides with all the slots. (If you don't hit a slot dead-on, the hole is miserably screwed up.)

If you haven't done it yet, I'd definitely go with Doug's LED mod or use the higher CCS current with the resistor bias - I think Doug is calling that the WE connection? It's a different amp when you do that.

In any event, the plans are definitely to include a custom-machined case with the eventual kits. That should alleviate the issues for those of us who are tool-challenged.

[n_maher]

Thanks guys!

Tom could you summarize the new recommended CCS settings?

[Nebby]

We were trying to keep from putting any holes in the bottom of the case and I got fed up with trying to drill through the sides with all the slots. (If you don't hit a slot dead-on, the hole is miserably screwed up.)

Any particular reason you were avoiding putting any holes into the bottom of the case? I drilled holes in the pcb directly underneath the transformer and planned on drilling a few holes in the bottom of the case under the transformer to provide vertical airflow, with side vents as exhaust.