Lo Watt p/p amps

[10thTx]

In an effort to give back to this forum for the help it has provided to me, I want to share some ideas that I've worked on with the help of DummyLoad on the Hoffman forum.

I've built the amp in the schematic below.

Many of the ones listed in this link are proposed amp designs that are not built yet.

http://www.el34world.com/Forum/index.php?topic=12526.0

With respect, 10thx

[selloutrr]

Thank you,

I'm noticing some strange labeling in the PI tube. and Output tubes.

Based on the schematic labeling the amplifier uses 2 tubes for the PI. Shouldnt it say V3A (1,2,3) and V3B (6,7,8 ) assuming it uses a standard 12A_7 to create a 180 degrees out of phase - push pull.

the labeling for the Output tubes would then be V4 and V5

the pentiode and triode labeling is not needed. you could however indicate the model of all tubes. i.e. 12A_7, 6V6, EL34, EL84, etc.
the E"C"L84 is a brand indication not model. most likely indicating it was manufactured in China.

why is the output transformer 4 ohms yet pushing an 8 ohm speaker? Hammond makes over 3 dozen models that will offer the same performance and give you multiple impedance taps to safely match ohm loads. running impedance mismatch can cause over heating and stress on the iron and speaker leading to premature failures. (each to their own, however mismatching is not covered under warranty repair)

It's also a good idea to document the transformer voltages. As well as adding the amperage draw of the fuse (size) on the schematic placed before the power transformer.

[RJ Guitars]

I had to look up ECL84 to find that it is a novel triode-Pentode... news to me! This is an old school NOS tube not a variant of the familiar EL-84.

Do you have any photos, clips or additional details on the amp? How many watts?

I love low power Push/Pull but I have found that because of the way our hearing works tone is proportion to volume which is of course proportional to watts.

Curious to learn more,

rj

[selloutrr]

The triode side is similar to a 12AT7 at about 65
ECL84 is 4Watts MAX
intended to run in Class A1

Price - $9 - $27 each

[renshen1957]

Thank you,

I'm noticing some strange labeling in the PI tube. and Output tubes.

Based on the schematic labeling the amplifier uses 2 tubes for the PI. Shouldnt it say V3A (1,2,3) and V3B (6,7,8 ) assuming it uses a standard 12A_7 to create a 180 degrees out of phase - push pull.

the labeling for the Output tubes would then be V4 and V5

the pentiode and triode labeling is not needed. you could however indicate the model of all tubes. i.e. 12A_7, 6V6, EL34, EL84, etc.
the E"C"L84 is a brand indication not model. most likely indicating it was manufactured in China.

why is the output transformer 4 ohms yet pushing an 8 ohm speaker? Hammond makes over 3 dozen models that will offer the same performance and give you multiple impedance taps to safely match ohm loads. running impedance mismatch can cause over heating and stress on the iron and speaker leading to premature failures. (each to their own, however mismatching is not covered under warranty repair)

It's also a good idea to document the transformer voltages. As well as adding the amperage draw of the fuse (size) on the schematic placed before the power transformer.

Hi,

ECL is a European designation for a dual Triode tetrode/Pentode tube. The schematic is correct. E refers to a 6V3 heater, C refers, L Output tetrode, beam tetrode or pentode.

The phase inverter uses one triode from each tube and the power tubes are the other half of the each respective bottle.

Transformers are wound to ratios. A 1,000 to 1 ratio would yield a primary of 8,000 ohm primary/8 ohm secondary with an speaker with a nominal 8 ohm specification, and 4,000/4 ohm with a 4 ohm speaker.

Transformers can have multiple secondary windings. A mismatch might affect bandwidth, but guitar amps do not necessarily have wide bandwidths to begin with, guitar amps are not Hi Fi amps.


Best Regards,

Steve

[es345]

Transformers are wound to ratios. A 1,000 to 1 ratio would yield a primary of 8,000 ohm primary/8 ohm secondary with an speaker with a nominal 8 ohm specification, and 4,000/4 ohm with a 4 ohm speaker.

just to clarify:

the winding ratio is the square root of the impedance ratio. In your example - impedance ratio 1000 - the winding ratio is 32

[10thTx]

5879 pentode into a 12A_7 into the triode LTPI of the ECL84 into the pentodes of the ECL84. The link I provided in the first post gives more information and editable schematics/layouts.

Speaker/OT impedence mismatch was intentional to suit the ECL84 tube. The OT has an 8 ohm tap & I purposely used the 4 ohm. I have never had a tube amp with an OT problem doing this & have used amps for yrs like this.


There is a thread about this specfic amp along with layout here:
http://www.el34world.com/Forum/index.php?topic=12488.0

I paid $1.80 each for my tubes. And Ebay has them quite cheap and much less than $9-27.

With respect, 10thtx

[10thTx]

I've been tweaking this amp slowly trying numerous tweaks and sometimes returning it back to original.

The ECL84 tube seems to be very bass and especially mid accented from what I hear.

So, I kept changing things to add treble but added smoothing caps to keep it from having that ringing/chimey tone (which I don't care for). IF you like the ringing/chimey tone ...... don't use the 10pf caps or the 220pf cap from V2-1 to V2-3.

These mods added smoothness and removed some of the mids that had some grit or ringing/chime to it. FWIW, I typically don't care for a chimey EL84 tone.

IMO, it plays very transparent and is quite touch responsive.

Just thought I'd share the update for anyone interested.

with respect, 10thtx.