Tubelab Simple P-P

[tubelab.com]

for the 6CW5 what would you think of the Edcor CXPP series? They have a 25W/3.4k ohm, bt it only has 4 ohm output, and they have a 30W/3.8k Ohm with 4/8/16 taps

It is unfortunate that the 3.4K transformer is only available with a 4 ohm secondary, since that would be my first choice. I don't know if they would make an 8 ohm version if requested. The 30W 3.8K transformer would work, but it costs more. Another possibility is the 7.6K to 16 ohm 25 watt transformer. This would reflect a 3.8K load to the tubes with an 8 ohm load. I don't have any of these transformers to try, and I am not likely to be ordering any in the near future, since I have several usable transformers here.

What do you think of the Antek AN-2T230 (230V/200VA) in the application of the 6CW5. It that overkill and too much for the tubes?

The Antek 1T200 that I have results in a B+ voltage anywhere from 219 to 230 volts depending on line voltage. That makes for a cool and conservative running amp, but it only makes about 14 WPC. I let it run at 15 WPC (visible clipping) with a 20Hz sine wave for about an hour and a half. Nothing was hot. The Antek was warm, and the $6 Triad choke was warmer, but not too hot to hold. I realized that I was cranking 300+ mA through a 240 mA choke, so I tried a 300 mA Triad choke. It got almost as warm.

I tried the "isolation" transformer that I had and found out that it isn't an isolation transformer. It puts out about 260 VAC which results in 315 volts of B+. Red plate came in about 1 minute, so I shut it off. I turned the transformer around to get 209 VAC resulting in 244 volts of B+. The amp works fine at this level. I still don't know if a 230 volt secondary would be OK, and I am not sure if the Antek 2T230 will actually produce 230 VAC. I might just order one and test it.

[tubelab.com]

I removed the board and made a spreadsheet with all of the component values that are currently in the board as it exists today. Of course after I did that I found out that .xls is not a valid attachment extension to post here and I don't have winzip on this computer. I'll figure that one out tomorrow.

I will be placing orders from Mouser and Digikey for some more components to try and to build a few more boards. Some component values are still being tweaked.

I then reconnected the board up to my variable power supply and decided to have some fun exploring the limits of some of my 6CW5's. This is what I found. The board is wired in pentode mode with the screens tied to B+ through a 100 ohm resistor. I may raise this value and repeat some experiments tomorrow. The OPT's are surplus 6600 ohm guitar transformers with an 8 ohm load on the 16 ohm tap for a 3300 ohm load. Frequency response is 6Hz to 45 KHz at 10 watts.

I fed the board several sets of GE branded tubes. They are very consistent and all will handle 280 to 290 volts. Power output is 24 to 28 watts at 5% distortion.

I tried the Sylvania "mystery tubes". They are marked 6CW5 but they have something else inside. That something doesn't like to go beyond 250 volts and the screen glows at 250 volts. Plate and screen glows at 275 volts and amp distorts at any power level. Beware, these are useless. The glass is darkened and there are 4 rectangular holes in the plates. The plates are not the typical 6 sided 6CW5 / EL84 shape.

I found 3 "Hewlett Packard by Amperex" tubes that have the Mullard date codes on the bottom. These crank. They work OK at 280 volts and made 30 watts at 3% distortion!

I found some "Hewlett Packard by Amperex" that are marked "made in Japan". These work at 270 volts and make 25 to 28 watts.

As expected the RCA "made in Canada" with the small plates glowed at 22 watts output.

I decided to go in the other direction and find out how low the board will go. The board will make 3 WPC with a 150 volt supply. The distortion at 1 watt was in the .5% range even with this low supply voltage. This makes this board an excellent choice for a hybrid super tube driver.

[SigloOne]

What are the tubes in the front end of the circuit?

[Ty_Bower]

Originally Posted by tubelab.com

The driver tube is a 12AT7.

[SigloOne]

I am pretty excited, my Siemens 6CW5's showed up today!

[SigloOne]

Anything new in the world of the Simple P-P?

[tubelab.com]

Anything new in the world of the Simple P-P?

During the first week of September I created a preliminary parts list and placed orders with all of the usual suppliers (DigiKey, Mouser, Allied, AES and others) for components. The intent was to have them all delivered this week so that I could be taking all of the pictures for the assembly manual this weekend. As of today I have not received anything. I just got shipment confirmation from Mouser yesterday for an order placed last Thursday night. They won't be here until next week and most of the resistors were ordered from Mouser. Guess which parts go in the board first?

I have decided to to a small parts package for the Simple P-P. For this reason I want to use the exact parts that will be in the package for the pictures. The Simple SE will follow shortly. The parts kit will consist of everything that goes on the PC board except the tubes themselves. This decision has put a $1K dent in the Tubelab credit card, so the orders to the parts distributors was rather lengthy. I can't blame them for being a little slow even with the holiday, but almost a week for 2500 resistors, 400 caps, and several other components in small quantities.


My original plans would have me driving north right now, but that has been delayed for a week or two due to complications in Sherri's moms treatments. I will probably spend some time this weekend optimizing and testing the board for EL84's and 7189A's. The build photos will happen as soon as the parts arrive. I can put the manual together on my laptop wherever I am.

[booangler]

George,

Sorry to hear there are continued issues with Cherri's mom. My mother in law was ill a few years back now and it is an arduous task at times. I wish you the best.

Can I assume that you will update us here when you are ready to start taking orders.

Alan

[tubelab.com]

I got this in an email from Mouser. "To expedite your order, we upgraded it to ship via UPS 2nd DAY AIR at a total cost of $22.83. We paid for the upgrade and only charged you the rate of UPS GROUND SERVICE." It still won't be here until next week. Could thay be reading this?

Sorry to hear there are continued issues with Cherri's mom. My mother in law was ill a few years back now and it is an arduous task at times. I wish you the best.

She exhausted all conventional cancer treatments almost 2 years ago and was basically told to go home and die. She was accepted in a clinical trial (human guinnea pig experiments) and they have been able to keep the cancer from spreading but they can seem to kill it. The problem is that she lives about 70 miles from the treatment center and must be driven there every week day for 3 weeks on then 2 weeks off. That has become Sherris job for the last 15 months.

Can I assume that you will update us here when you are ready to start taking orders.

I will post the assembly manual and several other updates on the web site as soon as it is done. Of course I will update this thread as progress occurs.

[millerlitescott]

Looking forward to this amp. I like the idea of a kit. Thanks George for all you efforts. Prayers sent for Sherri's mother.