A Direct-Coupled Amplifier with Cathode Follower

[brians7]

I am thinking about building this for my first amp. You guys have any thoughts Thanks Brian
http://diyaudioprojects.com/Technical/P ... Amplifier/

[Geek]

Hrm. I've played with cathode followers like (not those tubes) that and wasn't disappointed.

If Gio put it on his site, it's unlikely to be a lemon.

Cheers!

[brians7]

The schematic is pretty specific about the output transformers. Is says (It is essential that the primary of the output transformer have a resistance of approximately 250 ohms, as the resistance of this winding determines the grid bias for the 6V6.The primary impedance of this transformer should be from 5000 to 6000 ohms) I have looked and the only thing close is Edcor GXSE-10-8-8k it has a DCR of 255 Ohms. So my question is the 8k going to be ok here. Thanks Brian

[soundbrigade]

I have tested that schematic and it worked. Maybe because I didn't pay much energy to de-hum the setup it was a bit noisy.
I can shere the photos I took. Note the 6SJ7 (metal canned).
I should add that cathode copled amps also gives a certain amount of feedback.

[brians7]

Thanks Magnus. I do not see the Ducky. Does that mean that anything?
Here is the power supply that I built. Thanks Brian http://s292.photobucket.com/albums/mm24 ... 15_147.jpg

[battradio]

255 is close enough , cathode resistors used to always be 20 % so 5 ohms is close enough .

[soundbrigade]

I have had an idera of starting all over again and go for a Cathoded 6V6-SE. Especially as I propably will sell a pair of 6V6s to a guy who wants to build a guitar amp., so I will have two left for myself. Got some 6SJ7 from various project ideas.

By the time I tried this amp, which by the way requires extremely few components, the Quackti hadn't yet found his way to my place.

[brians7]

The truth be told I found this amp schematic wile searching the web for a amp that could be built with all metal vacuum tubes. I have some metal 6V6's I will need to pick the others up.

I have a couple of ? before I order the transformers.
Should I use the 5Z4 Rectifier - 5L - 5.0 - 2.0 - 20 - 125 - 350 - metal low drop 5Y3 and (275-0-275) power transformer to get the B+ to 335v

Or the 5T4 Rectifier - 5T - 5.0 - 2.0 - 45 - 225 - 450 - metal 5U4 and (300-0-300) power transformer to get a B+ of 335v

Also is the any objection for me using 8000k output in place of the 6000k
output transformers? They are the only ones that I can find that are close to the required 250 ohm DCR. Thanks Brian

[soundbrigade]

Talkin about heavy metal, Mapletree Audio Design started off with a 5W PP-amp (12A6, 12SJ7 and 12SC7 all metal) nicknamed STEALH. Then came the 6V6-Stealth, a 6L6 (or EL34??) and latest model is a KT88.
I guess the 6V6 version could be made as an all metal amp.
I can see if I have the diagrams available somewhere if you're interested.

Btw, my 12A6 all metal jacket looks like this:
http://www.pastisch.se/tubes/images/stealth-18.jpg

(Note that I swapped the metal 12A6 for the GT-version with window blinds as the metal tubes was behaving strangely).

[brians7]

So I ordered the transformers today. I went ahead and got all Edcor stuff.
I got the XPWR007-120 Power transformer for a 120V, 60Hz. line to 550V (275-0-275) at 200mA center tapped, 6.3V at 6A and 5V at 3A. Using the 5Z4
Rectifier I should be able to get the B+ close to the required 335v. Brian

[HK]

I built this amp and it sounds good.


You can plug in 6F6 6L6 or 6V6.


Is rather important to use an output transformer with a dcr of 250.

[HK]

So my question is the 8k going to be ok here. Thanks Brian"

Brian, the bass will be slightly cleaner, the distortion lower and as the Greeks say {no free lunch} slightly less power.

The output transformers you want to use are the exact same ones I am going to insert.

When I built that one, all I had @ the time was Edcors no bell 10 watt 5K into 6 ohm.


The DCR is NOT correct as you may assume and is rather hard on 6V6's, in fact I use the amp to stress test 6V6's as it causes 1 in 4 to redplate unless I use 5Y3's or 5R4's instead of the 5V4's I wanted to normally use.

I will send photos on my other computer as the Linux am using right now is not set up {yet} for USB photos.

[brians7]

Hi HK
It is good to here that you had success with your amp. I would love to see your pictures epically nude ones (the under side wiring) of course. I have just about everything ordered. I will be using 1/8" x 12" x 12" 6061 Aluminum Sheet for the top and bottom plates.
I have another ? What resistor if any would I use to replace the 250K pot?
Thanks Brian

[HK]

Brian, am having difficulty uploading photos here. I can send if you give me your Email address.


Have seen others do it so am just assuming just plain ignorant {smile}.

Ken[/img][/code]

[brians7]

So I got my shipping notice from Edcor today. It has been tuff not drilling the chassis but Tom said no chassis drilling till you have all the parts. Would anybody like to tell my why the 6SJ7 screens needs those two bid 10w resistors? Brian