• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

I want to build an inexpensive EL 84 integrated amp with a phono section.

pete1729

Member
2009-01-17 7:11 pm
I have nearly sorted out the Lafayette 236A that I recapped a month ago. It sounded great for a little while but one channel has gone a little wonky. I'm going to burrow into it again later this week. I think I'm just going to replace all the resistors in it, a total of 60 of them.

It sounded so good while it was working, it got me to thinking "maybe I should just build one from scratch?" One of the advantages I have is that the unit I have was a kit amp and I have the original assembly manual. One of the disadvantages is that it uses 7199 drivers, which are as yet unreissued. Also, while I can sling solder, read a schematic, and not electrocute myself I still am well aware that I'm usually in over my head.

So here are a couple of questions;

There is apparently a simple way to substitue 6GH8A's for 7199's. Should I consider doing this if I plan to clone my Lafayette? Or are the 7199's magic?

How do I choose transformers? Or even volume pots?

Does there exist a well sorted schematic for a 10+ wpc EL84 integrated with a phono section that I should look at instead?

Thanks!
 

Tesla88

Member
2011-12-21 8:37 am
Italy
For 7199 issue , you can use a 6GH8 but i'm not sure about operating point to get the lower distortion from the pentode section , anyway i read good things about 6U8 tube (aka ECF82) , cheap and good sounding ...
I'm building a Dynaco ST70 , so i'm intrested about 7199 replacement!
 
Go to audiokarma.org and register. Then look post #7 at this link:
6GK6/6BL8 schematic help.... - AudioKarma.org Home Audio Stereo Discussion Forums

Build that circuit using 6GK6s instead of EL84s. The 6GK6 are only $8.00 each at Vacuum Tubes - Audio Tubes - ESRC Vacuum Tubes - Electron Tubes. The 6BL8 may perform a little better than the 6GH8, and they are only $5.00 each.

If you decide you want to build this, I can help you with transformer selection, and how to implement a volume control.

Build a separate phono preamp, take a look at the Budgie, found here:
diytube.com • View forum - budgie mm


How do I choose transformers? Or even volume pots?

Does there exist a well sorted schematic for a 10+ wpc EL84 integrated with a phono section that I should look at instead?
 
Why not build a more modern design with in production tubes as those out of production ones will quickly run out as George of tubelab has discovered.

You could copy his Simple PP EL84 amp or buy the PCB or even the kit of parts to populate the board. The driver tube a 12AT7 is affordable @ $10 and EL84/6BQ5 can be bought for as little as $10. Plus lot's of tube rolling is possible!

Another one to copy or buy the PCB is diytube's ST-35 clone as it uses the common 12AX7 & !2AU7 or 12BH7 or ECC99 in the inverter position. There is also the original ST-35 also & the 7247 ( half 12ax7 & 12AU7) is in production again from EH & JJ.

For the best in sonics on the easy to drive output tube amps like 6V6/EL84/7591 Dave Gillespie's EFB mod (lot's of info at diytube in the ST-35 section under enhanced performance) , increased output tube life, 2-3 w/CH more power add his fixed bias
It can be done for $10-20.

Randy
 
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