CJ 11 layout

[Auke Jolman]

Hi All,

In the attachement I added a CJ 11 schematic and the corresponding layout. I've changed the wiring off the standby switch. The transformer I'm planning on using doesn't have a CT for the 5v windings. Also I added heater elevation.

Could somebody be so kind and look over the layout and point out any error or better way to put the layout together?

Also I would like to know what changes I have to make in order to use 6BM8 output valves.

With regards,

Auke

[shooter]

in order to use 6BM8 output valves.

Here's an example of a 6BM8.  look at reply #24
study the layout also to get a sense if you're on the right track

http://el34world.com/Forum/index.php?topic=21989.0

[tubenit]

I am going to suggest that you look at using a 5Y3GT instead of a GZ34 to get the voltages for the 6BM8 plates closer to 320v if you're using that power transformer.

Then you'd probably need to change the 22k resistor in the B+ rail to something like 4.7k to 10k to keep voltages up on the preamp and maybe the 10k down to 4.7k . You'll have to experiment with that, but those might be good values to start experimenting with.

Remember the 6BM8 tube has a pentode (power tube) and a triode that you can use for the LTPI .......... IF you want to.  Nothing wrong with using a 12A_7 for LTPI and just the pentode if you wish to go that route.

IF you want to look at how to use the 6BM8 pentode and then the triode for the LTPI,  look at the recent HoSo56 thread.

With respect, Tubenit

[PRR]

> use 6BM8 output valves

With 290VAC, your DC will be near 400V. The 6BM8 will be far happier nearer 250V. (You can also run good old 6V6 at lower voltage if you want 6BM8-like power).

I think you want another power transformer. If you are married to this one, you want a couple 1K 10W resistors to drop voltage.

[Auke Jolman]

Thanks for the replies so far. Much appreciated.

First of all, I think I've made a mistake with how I've drawn the standby switch. When I want to use a standby switch (better not?) , then the switch has to placed after the first reservoir cap, right?

In order to use 6BM8 tubes with HT 250 V, which PT will be suitable. I've look at a bunch but couldn't find one.

Looking at the HoSo56 schematic/layout, I noticed that there's a 290-0-290 PT drawn. I'm guessing the rect. tube is a 5Y3GT to get the HT down to 320 V in conjunction with the 1k res for the plates. Further more I've got to change the grid res. to 8k2 instead of 1k5.

When I would be using 6V6 with a HT 250 V, what would be an estimate for the wattage?

With regards,

Auke

[tubenit]

I ran 6BM8 tubes for several years at around 310v on the plates with no problems.

A PT with 250-0-250 using a 5Y3GT would give about:      250 x 1.1 = 275 volts.

A PT with 275-0-275 using a 5Y3Gt would give about:       275 x 1.1 = 302 volts.

with respect, Tubenit

[PRR]

> 6V6 with a HT 250 V, what would be an estimate for the wattage?

Read data sheets!

http://www.mif.pg.gda.pl/homepages/frank/sheets/201/6/6V6.pdf

Later sheets show 10W for this condition. (@ 5%THD)

[Auke Jolman]

Hi PRR,

You're right off course, that I should study datasheets....

But I get confused when doing so.

The datasheet for 6BM8 shows 1,8 W at 300 V and a plate load of 7k. Am I correct in assuming that in PP that doubles to 3,6 W. The HoSo56 schematics shows 9 W.

For 6V6 in PP at 250V and a plate load of 10k it reads 10 W, so 20 W in total. So how does this compare to the output off 6BM8 in PP

Clearly my knowledge is falling short. Is there any good reading material to up my understanding of this subject?

[tubenit]

For cathode biased 6V6's,  I'd figure anywhere from 10-15 watts or so.      (Silvertone 1482/Dano Centurian-10w   to  5E3 around 12-15 w)

For cathode biased 6BM8, I'd figure somewhere between 7-9 watts.           (HoSo56 or mini-Bassman)

with respect, Tubenit

[PRR]

> The datasheet for 6BM8 shows 1,8 W

You mean the Svetlana sheet. I too am confused.

6BM8 is a ECL82. Philips 1960 is contemporary documentation/sales info. It is dense and technical, yes. Page 6 shows push-pull self-bias. 200V and 10Kct gives 10.5 Watts output.

[Auke Jolman]

Thanks PRR. Indeed I was looking at the Svetlana sheet. I really thought I was loosing it

I read the pages that ValveWizzard has on PP and SE output tubes and tried to work it out with drawing loadlines etc. Didn't get the results I was expecting, so I guess I have to do it all over again and try to figure out what I did wrong.

Has anybody taken the time reviewing the layout I came up with? It will be much appreciated.

[darkbluemurder]

Auke,


I briefly looked at the layout and it seems fine as far as connections go. A couple of things I would do differently:


- I would put the 1k5 gridstoppers directly to pins 5 of the output tubes.
- I would put the 470R screen grid resistors between pins 4 and 6 of each output tube. This will allow you to put the cathode cap on the output tubes away from the cathode resistors - these get hot which the cap does not like.


I am at mine at the moment. I got the transformers wired and the board populated and in the chassis. Now it's just (!) wiring up the tube sockets, pots and jacks and then the final testing.


Good luck with yours,
Stephan

[darkbluemurder]

Meanwhile I finished mine - it was quite a while ago since I finished my last amp. I can very much recommend this build as I think it sounds great. The tweedy character is there along with plenty of gain if needed. The boost switch is essential to me in getting cleaner tones but other than that I don't see a reason for further tweaking at the moment. I stayed close to the schem except for adding a 25k mid control instead of the fixed 6k8 mid resistor. Cool little amp project.


Parts used:


- old Russian 6V6s from the 80s
- 18 Watt power transformer
- Mercury Magnetics Deluxe Reverb transformer (which I had leftover from another project)
- 2 JJ 83S preamp tubes
- ERO Roederstein coupling and bass/mid caps
- silver mica for treble and bright caps
- tantalum cap for the anti-bright cap on the volume control
- carbon film resistors in the signal path
- first a 5Y3 rectifier which gave me about 330V on the 6V6 plates, then I switched to a GZ34 which I prefer.

Cheers Stephan

[Auke Jolman]

Hi Stephan,

Good to see that you are happy with the amp.

I have yet to start on the amp. I've got exactly the same OT. Still have to decide wether to use 6v6's or 6MB's. Further more I'm planning on using a 100k pot for mid. For me it is important to keep the wattage down a bit. I can do this by lowering the voltage as suggested earlier.

I have been using JJ 6v6's on some projects. For some reason they are not to my liking.

I will be posting some progress reports as the build comes along.

[darkbluemurder]

Hi Auke,


For even lower power you could consider the 6K6 or the 6AG7 instead of the 6V6. The problem is if you are going too low with the voltages this could adversely affect the preamp and PI. But ultimately it is all personal preference.


The JJ 6V6 S sound a bit darker than other 6V6 tubes. They are a good solution for amps with high voltages on the plates. I had a quad of them for some time in my 100W Marshall that has 500V on the plates. The JJ 6V6s did not seem to mind but I put the EL34s back in since I lost quite a bit low end going to the 6V6s.


I have done a minor tweak to my CJ 11. I put a 1 meg grid stopper before the PI as recommended by ValveWizard. I definitely second this recommendation as it took away some brittleness I was hearing with single coil equipped guitars, especially on the neck single coils. It does not have less highs as such but they are less ice picky, which is a good thing. And it is also a good thing I am still annoyed by ice-picky highs because this means that my hearing is not completely gone yet :).


Cheers Stephan

[Glenn]

Sorry I I figured out my own question