Recommended EL84 amp designs?

[noviygera]

Hi,

I'd like to try an EL84 based amp with at least 15watts /ch. Any suggestion for the best candidates?
My first thought - Dynaco ST-35 kit..

thanks,
Herman

 

[aardvarkash10]

A topic canvassed on regular occasions, generally with a list of the usual suspects.

I find the search function useful...

 

[petertub]

Hi,

I'd like to try an EL84 based amp with at least 15watts /ch. Any suggestion for the best candidates?
My first thought - Dynaco ST-35 kit..

thanks,
Herman

If you really need 15w/ch then i suggest you look for EL34/6L6/6550 class
of amp that can deliver 15w/ch and still have peak margins.

 

[Eli Duttman]

Herman,

Consider "copying" the power section of the Sherwood S-5000. That design squeezes 20 WPC out of PP 7189s.

The Russian 6Π14Π-EB (6p14p-ev), AKA EL84M, is a true 7189 equivalent that's tough as nails, has good sonics, and is affordable.

The 7199 Sherwood used is "unobtainium". However, any of the 6BL8/6GH8/6U8 group is a satisfactory substitute.

 

[artosalo]

I have built many different sort of PP amplifiers at power level from 10 W to 100 W with Dynaco style front end by using soviet made 6F12P triode-pentode.

Attached is the schematic with 6P43P-E (EL86 / 6CW5).
This amplifier produces some 23...25 W at UL, 5k OPT and 300 V supply voltage.
With a pair of EL84, 8k OPT and 350 V supply voltage, more than 15 W is available.

 

[mbrennwa]

Take a look at the Baby Huey.

 

[Shef]

Attached is the schematic with 6P43P-E (EL86 / 6CW5).
This amplifier produces some 23...25 W at UL, 5k OPT and 300 V supply voltage.
With a pair of EL84, 8k OPT and 350 V supply voltage, more than 15 W is available.

Is that a Toroidy OPT on last photo?

 

[Bandersnatch]

Since EL84 also make good signal tubes, try 6550 finals...🙂
cheers,
Douglas

 

[globalplayer]

+1 for 6L6.

 

[noviygera]

Thanks for all responses!

10watts/ch would be the minimum. I have a Dynaco ST-70 and specifically want to try a good el84 or similar tube, for a change.

 

[Fenris]

Lots of good designs on here. Red Light District and Baby Huey come to mind. Broskie has a good basic EL-84 design that I've used (in a modified version).

 

[Eli Duttman]

Thanks for all responses!

10watts/ch would be the minimum. I have a Dynaco ST-70 and specifically want to try a good el84 or similar tube, for a change.

An ultralinear (UL) mode "El Cheapo" produces approx. 12 WPC. Any 6V6 family tube can be used with the parts values shown. The O/P tube bias network has to change, if EL84s are to be used.

There is some "magic" in "12" W. multi-grid power O/P types.

 

[artosalo]

Is that a Toroidy OPT on last photo?

Yes, this:
TTG-6AS7PP - Tube output transformer [5kOhm] 2x6AS7G / 2x6N13S Push-pull or similar - Shop Toroidy.pl

 

[goldenbeer]

Since EL84 is so easy to drive, you can go for some neat tricks

• Input / drive stage can be a dc coupled split load inverter rc coupled to the EL84 finals
• UL 20-25% will preserve almost all output power and significantly linearise the output stage and drop Zout
• You can efficiently use cathode FB around the OPT to further linearise the output stage
• You may bootstrap the input stage with some pfb from the EL84 finals
• Some 10~15dB of global nfb around the circuit will then clean out all cruft without doing too much havoc at the frequency extremes.
• Bias can be fixed, cathode, or even garter 🙂 for excellent hassle free auto biasing.

This should give you some very nice & clean 15WPC without requiring some exotic output iron.

 

[noviygera]

Thank you for the recommendations. Any existing kits or designs that implement the above?

 

[goldenbeer]

Don't know if any kits forsee these, but you can wire any kit to do so. The hardest thing would be to find the right OPT which supports the 20% tap and 4-8-16 ohm secondaries, which you need for the balanced cathode feedback.

 

[rmyauck]

Dynaco ST-35 can be built from kits and Triode Electronics has nice copies of the original output trans.

Dynakit sells original type chassis in SS & PCB's & Triode sells a bigger one with a bigger PCP that splits the driver tube (7247) into 2 of the same (12AX7 & 12AU7) for more tube rolling.

The EFB mod from Dave Gillespie adds to output tube life (through an advanced bias adjustment) and sonics.

Tronola Electronics has his info and PCB's

Tubelab's George Anderson sell's a really nice PCB also in which the EFB mod could no doubt be added and he has a nice simple driver tube the 12AT7.

His board can be set up for UL , Pentode , & Triode operation of the output tubes also and uses a tube rectifier with all it's advantages.

 

[mctavish]

I can fully reccomend that Broskie build, I have made 2 and both were excellent.

I also used 6V6GT tubes for a build and it worked out great. Two thumbs up🙂

 

[AuroraB]

Depends if you want a kit or build from scratch... There's several iterations of the old Mullard design around....

This one also has good merits.. although EL34...http://www.lundahl.se/wp-content/uploads/datasheets/amplifier_30wpp.pdf

 

[stonehome]

I second Tubelab’s SPP. Great as designed but I modified the board and paralleled 6HB6 sweep tubes.