• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

What SE to build

invaderzim

invaderzim

Super Member
I'm thinking of building another low power SE amp. I built the kegger KT88 and like it, running 6l6gc UL.
It will be for a small room so 3-8 watts will be fine.
I was thinking of the RH84, I don't have any el84 tubes but they can be had inexpensively.
https://rh-amps.blogspot.com/2013/02/rh84-amplifier-revision-2_26.html?m=1

There is also this 6l6gc, which I have a lot of
https://www.cascadetubes.com/the-6l6-spalted-alder-amp/

And this el34, which I also have tubes for
https://www.lundahltransformers.com/easy-to-build-se-amplifier/

Thoughts on the designs?
 
Register to hide this ad
None are my designs. Just curious what people think of those and if any have tried them. I can build an amp but I can't spot things that might be issues with designs.

The RH84 has the most info on it online.
The cascade tubes one is new and the Byrith design is older but doesn't seem to be a common build. It seems a bit more complex.

I have read some on the unset, it seems to be in the testing stages and I do better with a finalized design. I lack the test equipment to do my own tweaks. If I buy test equipment then it would eat the budget for the amp and I don't plan on building more after this.
 
Why not use Real Triode tubes?
Where are you going to source the output X-formers/
Cap coupled/? or transformer coupled. AC or DC?
 
Nyjblbob said:
Why not use Real Triode tubes?
Where are you going to source the output X-formers/
Cap coupled/? or transformer coupled. AC or DC?
Click to expand...

Expense, mostly, on the real triodes. It would be nice to do one I already have output tubes for. 2a3 arent too expensive but $300 for a bottom of the line pair of 300b tubes really increases the amp cost. And then any tube upgrades later would get crazy.
I was thinking of maybe lundahl for the outputs, but still open on that.
Transformer coupled and DC heaters seem to be more of a 300b thing.
Largely just looking for a nice sounding, fairly simple project to help stave off the winter depression.
 
spantou01 said:
The big ones like EL509 in triode,
Click to expand...
I have many fond memories of my friend who had an EAR EL-509 SET amp.
It was one of the best sounding home systems I ever heard Used Alon 4''s Speakers.
Nola should make them again and call it a Heritage Model
 
Tubelab's SSP amp board can be configured for many tubes. 6L6, EL34, KT-88, etc. He also sells an EL-84 board. I built the Tubelab 300B. It sa nice sounding amp. I'm gathering parts for the SEDG-1 EL84 se amp myself. It's pretty simple.
 
invaderzim said:
I'm thinking of building another low power SE amp. I built the kegger KT88 and like it, running 6l6gc UL.
It will be for a small room so 3-8 watts will be fine.
I was thinking of the RH84, I don't have any el84 tubes but they can be had inexpensively.
https://rh-amps.blogspot.com/2013/02/rh84-amplifier-revision-2_26.html?m=1

There is also this 6l6gc, which I have a lot of
https://www.cascadetubes.com/the-6l6-spalted-alder-amp/

And this el34, which I also have tubes for
https://www.lundahltransformers.com/easy-to-build-se-amplifier/

Thoughts on the designs?
Click to expand...

As hou can see! Much interest and many answeres

Please narrow your question.
 
invaderzim said:
Transformer coupled and DC heaters seem to be more of a 300b thing.
Click to expand...
No it's not. 45's 2a3's, 6a3's and 6b4's as well as many other triode tubes benefit transformer coupled
as well as AC heaters if implemented correctly
 
invaderzim said:
Expense, mostly, on the real triodes. It would be nice to do one I already have output tubes for. 2a3 arent too expensive but $300 for a bottom of the line pair of 300b tubes really increases the amp cost. And then any tube upgrades later would get crazy.
Click to expand...
I've used real triodes for two builds, one SE and one PP, using NOS output tubes that can typically be found for $15 to $30 each. Here's the SE one, which uses all triodes and puts out ~4 to 4.5 wpc, which is a bit more than the 2A3.

https://www.audiokarma.org/forums/index.php?threads/the-nuance-my-inverted-set-diy-project.990205/

The input tubes are also inexpensive. Strong to new testing used ones are plentiful. The least expensive were around $7.50 and the most I paid was ~$25.

The design could definitely be simplified. I tried a few things, like using a voltage regulator tube, just because I had never used one. Not sure if it offers any sonic advantage. And the PS, which uses a 5AR4, could also be done cheaper using the "cockeyed bridge" design that I'm using for my currently breadboarded project.

Come to think of it, I've also built another SE amp that uses all real triodes but it only puts out maybe 2 wpc.
 
Personally, I would build an SE EL34 amp, because I love the sound of that tube and there are so many good versions available. But an SE KT66 would be nice too.
 
I started looking at the RH84 a while back after building a Kegger/Blueglow KT88. It was pointed out to me how similar the schematic is to the KT88 so I started looking around again and have settled on doing a scratch build of Dave Gillespie DG-SE1.

It starts out as an exercise to optimise a Magnivox but the resulting schematic has been used by lots to scratch build.

Here's the thread....

https://audiokarma.org/forums/index...ore-out-of-the-8600-series-a-lot-more.665735/
 
Hyakuya said:
I started looking at the RH84 a while back after building a Kegger/Blueglow KT88. It was pointed out to me how similar the schematic is to the KT88 so I started looking around again and have settled on doing a scratch build of Dave Gillespie DG-SE1.

It starts out as an exercise to optimise a Magnivox but the resulting schematic has been used by lots to scratch build.

Here's the thread....

https://audiokarma.org/forums/index...ore-out-of-the-8600-series-a-lot-more.665735/
Click to expand...
Are going to build the fist, or second version of the DG1?
 
Hyakuya said:
I'm going with v2 of the schematic with a few changes to accommodate different PT, choke and OT's.
Click to expand...
Yeah, if you're doing a scratch build of that you should definitely consider using different output transformers. The ones he uses (not sure about v2) were mostly chosen for their size - they physically fit the tiny Magnavox chassis. That and they have 8 ohm secondaries. The stock OTs are 4 ohm, which is just less convenient since most home speakers are 8 ohms. If you use 8 ohm speakers with the stock OTs the load seen by the 6BQ5s is not optimum.

I modded one of the stock Maggies but, instead of replacing the OTs, I used 12BH7s instead of 6BQ5s. The 12BH7s work well with the stock OTs and 8 ohm speakers. That's the 'other' SE amp I was referring to above. It has about the same power output as the 6BQ5 version, but it's less than the 3w minimum that @invaderzim mentioned.

https://www.audiokarma.org/forums/i...0-or-8600-conversion-to-12bh7-outputs.824135/

Another SET to consider is the well respected Bugle 45, designed by Gordon Rankin. I built one of these too but, again, the 45 will only put out ~2.5wpc.

There is a kit being sold by Analog Ethos called the Legendarium that uses almost the exact same circuit as the Bugle but it's adapted for use with 2A3 output tubes, which will give you ~3.5wpc. @theflattire built one of them and he's been very happy with it.

Of course, neither 45s or 2A3s are cheap. The Nuance iSET I linked above sounds better than my Bugle and the inexpensive 6N6Gs put out more power than a 2A3.

If you need more power, another under the radar output tube to consider is the 1625. It's essentially a 6L6GC but it uses a 12v heater, a 7 pin base and a top cap, so it's not very popular. NOS RCA blackplates can be found for $5 or so. The same tube in 6L6GC guise will run you $80 to $100 each, if you can even find any. Most of the NOS ones have been burned up in guitar amps over the years.
 

Attachments

Here is an affordable single-ended stereo amp project that uses EL34’s in triode mode. The design is not an original, but inspired by a Music Angel Mini X3 EL34 amp that I picked up in Hong Kong on a business trip years ago.

The performance of the Music Angel Mini EL34 was not great; noisy (hiss and hum) and high distortion at low volumes. The input tube was a 6N2 capacitively coupled to the EL34 wired in pentode mode.

Surprisingly, the output transformers must have been wound with some care and consideration because the frequency response of the modified amp (without feedback) is out to 70kHz~80kHz (tube dependant), -3dB @ 1 Watt/8 Ohm. The low end goes down to 25Hz, -3dB @ 1 Watt. This is quite extraordinary for an inexpensive Chi-Fi amp. The output transformer only has a single secondary tap and the outside chassis is marked: 4~8 Ohm. I measured the reflected impedance for an 8 Ohm load and it came out to 4.33k primary impedance.

The main modifications to the Mini EL34 is the power supply, input tube circuitry, triode mode output (versus pentode) and various grounding issues. The power supply was a CRC design with marginal capacitance which was the reason the hum was audible on my >100dB all horn (bass, midrange & tweeter) loudspeaker system. I changed the design to a CLC with more capacitance to reduce/eliminate the hum. With my head inside the mouth of the bass horn, nothing is audible now nor on the midrange or tweeter horns either.

I’m using the 12AV7 in an SRPP circuit to drive the EL34. Since I always use a preamp to drive my amps, I did not need the high gain in the original Mini EL34 input circuitry (6N2) 0.5VRMS will now drive the amp to 1 Watt/8 Ohms and a little over 1VRMS will give you full power.

The original power transformer is 240VAC since I bought it in Hong Kong. The secondary voltage for the Mini EL34 is 155VAC and it configured as a voltage doubler. The power transformer shown on the schematic (Edcor) is a center tap model so you can use a standard full wave rectifier set-up for B+.

To clarify, I have not used or built a version with the suggested Edcor power transformer, but simulated it and the suggested (power supply resistor: Rps 50 ohm/10 watt) values on the associated schematic should be close. If B+ is not at the correct voltage, increase/decrease Rps in 25 Ohm increments until the voltage is at the nominal value on the schematic.
EL34SE_Svetlana EL34_Analyzer_1 Watt.png EL34SE_Svetlana EL34_Analyzer_Full Power.png EL34SE_Svetlana_12AV7_FR_1 Watt_8 Ohm.png
EL34 SE Stereo Amp_OE Power Transformer_v4.0.1_121722.png EL34 SE Stereo Amp_Edcor Power Transformer_v4.1.1_121722.png
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom