Tubelab Simple P-P

[noodle]

Any chance a bag of parts might also be available with the boards?

[tubelab.com]

Any chance a bag of parts might also be available with the boards?

I plan to do this, but not at first. There is just too much to do, Tubelab and otherwise right now. I must be out of town for 10 days in about 2 weeks. With only one weekend before I leave, it's not looking like the manual will be ready either. We will just have to see how things work out over the next few days.

Today I got about 1 1/2 hours to do some testing. I removed the power transformer and connected an external power supply so I could find the best operating point for several tube / transformer combination.

The data sheet for the 6BQ5 claims 17 watts for a pair with an 8000 ohm load. I found no combinations of voltage, current, and load imperance that produced 17 watts without screen grid glow. Best case here was 15 watts.

The Russian 6P14P did a little better, and the EI 7189A (which looked like the EI 7189A) was flirting with 17 watts.

I swapped in some surplus guitar amp OPT's, and installed 4 X 6CW5's. They have a 250 volt max, and at that max 20 watts is available. I listened to them through the much bigger OPT's. This setup rocks! 20 watts is still available at 20 Hz.

[rmyauck]

Great board for $35 George! Real NOS 7189A have different pinout right? Info I read could be wrong.
I bet you could add a plug in (short wires to it) simple CCS or powerdrive board later if one wished ? Could you use use the output tubes as drivers too, as I read EL84 are supper easy to drive? I read somewhere EL84 driving EL84 sounded pretty good. Keep up great work!

Randy

[tubelab.com]

The Russian 6P14P did a little better, and the EI 7189A (which looked like the EI 7189A)

That is a typo. It was late. The text should say that the EI 7189A (which looked like the Russian 6P14P) was flirting with 17 watts.

Real NOS 7189A have different pinout right? Info I read could be wrong.

The original 6BQ5 has no connection made to pins 1, 6, or 8. The 7189A uses these pins as connections. There are dozens of variations of the 6BQ5, 6BQ5A, EL84, 7189, 7189A, SV83, SV84, 6P14P and more, that may use one, two, or all 3 of these pins. If the socket is wired for a 6BQ5 and no connection is made to the "extra" pins, all of these tubes should be pinout compatible with the socket. The Simple P-P is wired in this manner. There is a wide variety of power and voltage handling capability among all of the variants and for this reason they are not all electrically interchangeable. This is particularly true with some of the Russian tubes being sold on Ebay as 7189A compatible.

[netbug]

Originally Posted by noodle

Any chance a bag of parts might also be available with the boards?

Another option that wouldn't require tublab stocking the parts would be a mouser project.

For example here is my gingertube baby huey project (it has some missing/changed parts so don't use)
http://www.mouser.com/ProjectManager...sID=5f46085321

[ChrisA]

Originally Posted by tubelab.com

...The board for a complete two channel amplifier becomes too big for economical fabrication and the thermal issues would compromize the reliability. So it seems that anything bigger than the Simple SE or the Simple P-P really needs to be broken up into multiple boards or "modules".

It seems to me that the simplest and lowest cost way to go is to do what Dynaco did with the ST35 and ST70. There is a small PCB that holds most of the components but not the power tubes. Those tubes are on conventional chassis mounted sockets and connected to the PCB with hookup wire. Yes I know the problem with that -- the final result depends more on the builder's skill and use of common sense to get the lead dress "correct". But that could be addressed by specifying shielded (coax) hookup wire and DC heaters.

The PP design that, I think would make the greatest number of people happy would be one the that could use a varying number of parallel output tubes. I'm working (slowly) on a guitar amp that does this. It uses four octal tubes but can also run with two. I'm adding switches to remove half the tubes and also for pentode/triode modes. A stereo version would have either eight or four power tubes.

When you change the number of output put tubes that are run in parallel you change the output impedance. This is addressed by using an output transformer with multiple taps. Commonly available OPTs allow for two doublings of the impedance. which is more range then you'd need.

But do people really need this much power? With the transformers I'm using I'll be "limited" to about 120W (in the single channel) but most of the time I expect to run with 2 tubes in triode mode which works out to about 30W of power. A 120W amp is insanely loud. In fact it can't be safely used without hearing protection. What's the point of a home HiFi system that requires ear plugs?

So, bottom line is that I think one could design a small PCB that could hold most of the components for a PP amp that could be rated at up to about 200 WPC (four KT88 tubes per channel) or more reasonable with two 6V6 tubes per channel if you keep the power tubes off the PCB.

PCBs are priced by the square inch. So you really don't want to pay for space between big octal tubes that is required only for air flow. The best use of a PCB is for the small low power components that can be "dense packed".

[tubelab.com]

Another option that wouldn't require tublab stocking the parts would be a mouser project.

A Mouser project is a possibility. I have had dozens of requests for everything from complete kits, to just a bag of all of the small parts that are used on the PC board. There are two reasons for this.

First, there are a sizeable number of builders who would rather not be bothered with ordering all of the parts, and would pay a small premium to be able to get them all in one bag or box from one source.

Second, and far more important are the international customers who either must find a suitable local source for all of the components, or pay the exhorbitant shipping rates that Mouser or Digikey will charge because they insist on using UPS or Fedex.

For the time being the USPS has a small flate rate box that is the size of a VHS tape that ships for the same price as the flate rate envelope I currently use to send a board. That means that if the board and the components are ordered together, the components ship for free!

There of course is the fact that the USPS is losing bucket fulls of money, closing post offices, and cancelling overtime for all of their workers, so they will likely cancel many of their most useful services or raise their prices.

Since I currently have a full time job that keeps me at work late most evenings, I just don't have the time to take on another project right now. Sherri lost her job, and could do a great job with this one, but she spends more time with her mom now than she does here.

[tubelab.com]

I am getting requests for schematics, board files, parts lists and all of the information needed to make one of these amps. Unfortunately, I don't have it all ready yet, but I am including the schematic and the PDF of the top layer of the PC board. I am still tweaking some component values, and figuring out what components must change when different tubes are used.

I will blow this amp up at least a dozen times in many different ways so that you won't have to. I will publish a provisional parts list here as it unfolds, but the final version that goes on the web site will be battle tested. I haven't even connected up my guitar yet. That is always good for some fireworks!

Example: 6CW5's rock, but they like current, and lots of it. It is easy to get 100 mA per tube without clipping, and running the amp into clipping at 20 Hz (26 WPC) managed to blow a cathode resistor. I don't know the total amp current yet because the 300 mA meter on my power supply was buried! I am guessing over 500 mA in hard clipping. Measurements on the surviving channel indicate that the cathode resistors see less than 1 watt with EL84's so 2 watt parts were used. 6CW5's subject the cathode resistor to about 2 watts in normal operation and a bit more than 3 watts when cranked to 11. So the parts list will reflect a 5 watt resistor with 6CW5's.

[SigloOne]

What are your impressions of the 6CW5 tubes as far as sound quality and distortion?

[tubelab.com]

What are your impressions of the 6CW5 tubes as far as sound quality and distortion?

I have been rocking the 6CW5's for a few days. I am convinced that they give me the best sound. I have always been a fan of low impedance tubes with a high peak current rating. The measured distortion and power output is the best of the tubes that I have tried.

This does not come without a fairly steep price though. The 6CW5 likes current, and lots of it, at a low B+ voltage like 250 volts. I am seing average current in the 380 mA range for the complete amp. Peaks go to almost 500 mA when you crank some Metallica! This is too much current for any common rectifier tube, and the board was not set up for solid state diodes. Power transformers with ratings to support this aren't common either.

Dumb blonde moment:

The current drawn by this board with 6CW5's is more than my old Fluke power supply likes to put out (current meter is pegged). I got this brilliant idea to wire two power supplies in parallel. Dumb idea. They fight each other and the current meters look like windshield wipers!

I am about to experiment with some power toroids as OPT's. I will report the results later.