New Project

[martin manning]

Excellent! I had forgotten all about that. I have the schematic Colossal drew up, which has some good ideas. Matt drives an EL84 directly, where I'm planning on a 6V6. I want to ditch the preamp out/power amp in, and take a line out from the output transformer. That will be driving either a resistive load or a speaker for a reactive load.

I have to pause for a few days until a new chassis arrives. I had Seaside make one up for me, but it is just not at all square. I've found a small Bud chassis that looks like it will fit. It's light gauge, but I believe I can make that work.

[Guy77]

Excellent! I had forgotten all about that. I have the schematic Colossal drew up, which has some good ideas. Matt drives an EL84 directly, where I'm planning on a 6V6. I want to ditch the preamp out/power amp in, and take a line out from the output transformer. That will be driving either a resistive load or a speaker for a reactive load.

I have to pause for a few days until a new chassis arrives. I had Seaside make one up for me, but it is just not at all square. I've found a small Bud chassis that looks like it will fit. It's light gauge, but I believe I can make that work.

Nice build Martin. I got hooked on Single Ended ODS amps last year and built several of them for friends.
I used an adjustable resistor to tailor the cathode resistor value to taste and then sub out a permanent resistor or keep it if you like and switch to different tubes buy adjusting the resistor!
I tried EL84, 6V6, 6L6 and 6550 but always went back to the 6L6 for the nice full bottom end sound!

20240308_183853.jpg

Here is a 6L6 version I built with a Hammond 270DX and 125ESE. plates running at 322v. This was well below limits of the 6L6 since it ran at only 7 watts clean output. I ran the plates at 180K and 120 K respectively and I threw in a Tweed deluxe style tone control for the Overdrive channel only. I did the full HRM stack that Matt did but ended up liking the simple Tone control instead. Clean channel got T, M , B controls. I found this Tone control to be one of my favorite mods for these Single ended ODS amps.

The 55 sec mark of the video below is the overdrive channel kicking in!
These are silver powder coated chassis in the ODS size format. If there are enough people interested I can get my machine shop guy to make another batch of 10 of them.

https://www.youtube.com/watch?v=jkt3vXuToDI

Sorry didnt mean to derail your thread just wanted to share the excitement I had with these amps!

Cheers
G

[martin manning]

No problem, it's all good input! Sounds good, too. Interesting you had success with a 6L6, what with its need for more drive voltage than an EL84 or 6V6.

[Guy77]

No problem, it's all good input! Sounds good, too. Interesting you had success with a 6L6, what with its need for more drive voltage than an EL84 or 6V6.

Thanks Martin, its my friend Kyle playing the amp. I would like to turn back the clock to being that young again LOL.

I was thinking the same thing you were about driving larger tubes but in the end it worked out.
I ran it with a 124 Classic tone stack and 100k slope with v1 and v2 A at 180K/5uf/2.7k and B at 120K/5uf/1.7k and was pleasantly surprised.

I started using transformers that gave me 400v on the plates and those gave the amp a tighter sound and some prefered those too.
To each their own taste, and the customer is always right lol!

I am sure yours will sound absolutely amazing!

Cheers
G

[pullshocks]

For my 6V6 SE power amp I followed the AX84 5 watt building block but with 302 volts on the plate due to a different PT and 5Y3 rectifier. Most say a tube rectifier is pointless with SE but I wanted the option to try it with different voltages.

The AX84 schematic includes a ability to tweak cathode resistance. After trying 5881, 6BQ5 and 6V6, I settled on 6V6.

AX84_5W_SE_Poweramp_Schematic.pdf

[10thTx]

Years ago Mat in Finland posted a SE ODS with no "phase inverter." By all accounts it sounded great

As an FYI, several of us on the Hoffman forum followed Mat's build and listened to his fantastic sound clips .................. and then tried building his SE amp using 6L6's. It didn't come close to the tone Mat got using EL84's.

With respect, 10thtx

[martin manning]

...tried building his SE amp using 6L6's. It didn't come close to the tone Mat got using EL84's.

Anybody try using 6V6?

[bepone]

i have built many champs with 6V6.. sound on lower voltage (300-310V) is great.. i already accumulated all the parts for higher gain champ, 2xECC83 + 1x6V6/6L6 which will be at June probably.

[rogb]

...tried building his SE amp using 6L6's. It didn't come close to the tone Mat got using EL84's.

Anybody try using 6V6?

I did on my EF86 SE, and 6L6

I think I might be finally done on this project!!!!!!!

Today I added a 470R and 47uF to the octal cathode pin 8, rather than running both sockets (separately) off the EL84 150R/220uF cathode.

I found I could use a 6L6 with no problems, OT/PT cool as you like, and have found the big clean tone I wanted so I probably don't need to build a clean version right away to fit in my cab. However, that doesn't mean I don't want to

Final tubes are:

V1 Mullard ECC83
V2 Mullard EF86
V3 Philips Miniwatt EL84
(V3 octal - any from Brimar 6V6GT, JJ 6V6, TAD 6L6)

My demo Visio has now expired, and TBH, I was losing patience with it, I spent hours trying to get the PS caps right only to mess up the layers and start again. I then realised how much else I had to do.

I will soon do the layout as I built it in JSchem, not so pretty but a heck of a lot easier. There haven't been many computer programs that have defeated me over the years but Visio

Thank you all for your patience with me, and all the help TAG members have given.

Tomorrow evening I will be in Finland and I hope to meet up with my miniHRM inspiration, Mat sometime I hope he has time for a quick chat anyway.

Regards
Rog

[martin manning]

I did on my EF86 SE, and 6L6

Thanks, Rog. So EL84 was your preference over 6V6? Was it a close call? I could be persuaded to switch, if that's the hands-down best tone. Planning for 6V6, my plate voltage is going to be quite a bit higher than Matt used, however. What primary impedance did you use?

[rogb]

I did on my EF86 SE, and 6L6

Thanks, Rog. So EL84 was your preference over 6V6? Was it a close call? I could be persuaded to switch, if that's the hands-down best tone. Planning for 6V6, my plate voltage is going to be quite a bit higher than Matt used, however. What primary impedance did you use?

It was 2011, I really don't recall but it was a 125DSE OT so I guess I used 5K?
I liked both tubes so had octal and noval sockets, I suppose 6V6 was a bit more headroom?

[martin manning]

Wow, time flies! I think 'll stick with 6V6. You're right EL84 has very low drive voltage requirement.

[pullshocks]

Any progress on this project/

[martin manning]

Thanks for the nudge... It's been sitting for a bit. I reworked all the drawings and hunted down the remaining hardware. Just need a day to focus on it now.

[didit]

Hello Martin --

What goals have you set for this SE power stage? Assumption has been HiFi but perhaps you want the HiTHD of a Champ et al. If you want something akin to "low power" Dumble/ ab763 then suggest exploring an output transformer with a hefty core and nominal impedance of 3.5-4k driven by 5881 or similar, or maybe the JJ 6V6 that's got some 6L6 characteristics. With a fair B+ voltage coupled to solid primary filtering (100uF), and perhaps even choke-based PI filter, you will get the low-end bandwidth and solid damping needed to achieve HiFi profile at around clean 7W. Anticipate you'll see that your preamp as-is or perhaps given minor obvious tweaks will readily swing it without the modest gain and drive of the PI. A silicon cathode follower would help.

You've the EE chops and tooling to run a pre-build design exercise, though you'll really need to think about how to model chosen SE OPT as manufacturers are sparse with the necessary inductance and impedance details to do so in a fulsome way. That is, unless you have a specimen you can place into a test harness. You might also spend a bit of time, assuming you haven't reading, in some of the more sensible SE HiFi threads on the forums focused on audiophile gear.

Small apologies for belated input, but life regularly limits my opportunities to add substantively to the conversations. Have fun and good luck regardless.

Best .. Ian