little Push pull amp

[fuzz]

Hi guys,

I have an unused hammond 125C in my stock. I used it in a small 1W tube amp using 12AU7 for the output tube. I've tried few preamp circuit and didn't like the sound of it , too dark and dull .

So I was wondering if there're any pentode tubes that can make a nice low watt push pull ? the OT is really limited and rated at 60mA/8W but maybe I could make something with small pentode as 6AU7 , 6AS5 that kind of old tube.

any ideas ? suggestions ?

best regards,

fuzz

[kagliostro]

ecl82 / 6BM8 ?

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6BM8

http://www.el34world.com/charts/Schematics/files/gibson/GA-8T.pdf

EDIT: may be you can also consider el95 as an usable tube

http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=EL95
http://www.nj7p.info/Common/Tube/SQL/Tube_query.php?Type=6DL5

About schematic for the el95 you can do a search also for ell80 amplifier, the ell80 is a tube with two el95 tubes inside

K

[tubenit]

I built a SoLow Watt amp of about 3-4 watts.  It used ECL84 tubes.  There is a lengthy thread here with schematic, layout and soundclips:

http://www.el34world.com/Forum/index.php?topic=12488.50

Look on the second page of the thread.  

Here is a soundclip of the amp playing a clean tone: 
http://www.soundclick.com/player/single_player.cfm?songid=11526416&q=hi&newref=1

With respect, Tubenit

[fuzz]

hi

thanks tubenit for the link , I read it a lot of good imformations. The 6AM5 looks interesting with a reasonable plate current (about 44mA) but seems hard to find compared to the ECL84 which is really cheap on ebay.

I think the low current of the transformer make it hard to find a suitable tube . Someone knows the tolerance of the Hammond transformer ? is that possible to push it a little bit (I know that the manufacter will say no  but maybe someone in here has experienced that).

[tubenit]

Have you looked at this somewhat lengthy list of low watt push/pull schematics and layouts here:

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

DummyLoad did much of the work compiling them and putting this together.

With respect, Tubenit

[heresrobert]

Fuzz,

Not sure how low watt you want to go. A while back, I built a two channel push-pull ECL82 amp. That was too loud for what I wanted as a living room amp. I then built a push-pull 6AK6. From the data sheets, it's a couple of watts and volume to spare for the living room. Both amps sound great through a plain Jane 12" speaker. I suppose if you want to go lower wattage, you could start with PRR's Third Watt schematic and make a "Two Thirds Watt".

Robert

[fuzz]

thanks tubenit for the links .

Actually I've few ideas for the preamp . I'd make something more gainer than usual , not hi-gain for sure but a kind of T-rex sound . I'll try to don't use tonestack , only RC filters for tone controls.

the output power isn't really a big deal , if I keep the idea of the preamp I'll put a master volume so 3 or 4W would be nice . Actually I'm limited by the output transformer so I'll make the amp around it. If no master volume, I'll use a power attenuator.

Even 1W is too loud for the living room , all is in the compromise 

[TIMBO]

Hi Fuzz, Tubenit is on the money with the LOW WATT amps and the ECL84 is a great cheep tube. His amp has a PPIMV so your able the keep the amp cranked at a low level. This is my build  http://www.el34world.com/Forum/index.php?topic=14048.0 Hope your able to find something to build but be WARNED one is not ENOUGH. 

[fuzz]

Looks nice, I'll read it.

In making researches I've found that the wem westminster used 2 ECL82 for 10W , is that possible to get 10W out of this tube in push pull configuration ?

the 1969 datasheet of philips says yes .

find something to build but be WARNED one is not ENOUGH.  icon_biggrin

you mean one amp ?

I know that, that would be me my third and the second isn't even finished (tweaking and always tweaking) . and I've build a tons of pedals (and on breadboards) . God I can't stop making those things !  

actually the problem is : never enough money  

[fuzz]

Hi ,

I've looked at datasheets and found that the EL95 could give a 7W little amp  and the current matches the specifications of the trnasformer.

I'll look futher if I can find few of these tubes on ebay for cheap.

Otherwise I'll go with the ECL84.

[smackoj]

Senor Tubenit; a few questions and a comment. I love the sound of this SoLo amp on your clip. I'm much more into the clean these days because I like to hear the tone of the guitar w/o driving the the circuits past the Swamp Ash, Walnut, Mahogany and Alder's aged flavor.
1. Could this be built using a PT that makes more B plus volts? Would I need to tame down one that makes apprx. 350 v?
2. I don't think I'm quite at the level of this build, so would it be possible to simplify your design and make it less parts and solder joints but keep the signature clean tone you have on the sound clip? I have a nice rev. pan I could use to keep that feature.

muchas gracias,  Jack D     

[DummyLoad]

6AM5 - 4.0W p-p; 250V B+; 24K load; Rk 600R @ 3W
6AR5 - 6.8W p-p; 250V B+; 15K load; Rk 240R @ 3W
6AS5 - 4.4W p-p; 150V B+; 9K load; Rk 1.2K @ 2W
6BF5 - 3.8W p-p; 110V B+; 5K load; Rk 68R @ 2W
6BK5 - 7.0W p-p; 250V B+; 13K load; Rk 68R @ 2W
6CU5 - 4.6W p-p; 120V B+; 5K load; Rk 75R @ 2W
6DS5 - 5.6W p-p; 200V B+; 12K load; Rk 91R @ 2W
6HG5 - 9.0W p-p; 250V B+; 10K load; RK 120R @ 3W  <<-- my favorite.

none of the above exceed the the 60mA 1/2 primary rating at full power. the 6HG5 pushes 9W but may do OK but may have weak lo-freq. repro.
considering the hammond has a spec of 8W @ 100Hz. lo-freq down to 50Hz @ 4W seem doable, 70Hz is what most guitar iron is rated at, and likely have a better response overall running 4-6W . the 6AS5 plan seems to be the easiest to implement - 120V PT will get you up around 160V B+ - close enough - run OT @ 10K load - again, close enough.

these seem like a nice set and reasonably priced.

--DL
 

[fuzz]

thanks DummyLoad  , I keep that list .

I realised that ther'is a lot of tube which can make the deal. Yesterday night I even looked at the 6SK7 as output tube .

actually low plate voltage isn't necessary . I think I've also the power transformer, it's curently used in an SE EL84 amps but it is to weak to give a proper 250V b+ at the anode of power tube. So I'll certainly use this for this projet .

my main concern right now is the availability on the market for the tube used in the amp. ECL84 seems to be in this case, EL95 less , I'll look for the others.

the power doesn't have to be big, 4 to 7W would be enough.

[tubenit]

1. Could this be built using a PT that makes more B plus volts? Would I need to tame down one that makes apprx. 350 v?

Look at the datasheets for the ECL84 maximum volts. Perhaps if you have a PT with 5v wiring, you could use a 5Y3GT instead of SS. Doing that would possibly allow a PT with higher voltage than what I used.

2. I don't think I'm quite at the level of this build, so would it be possible to simplify your design and make it less parts and solder joints but keep the signature clean tone you have on the sound clip? I have a nice rev. pan I could use to keep that feature.

You can use a paralleled 12A_7 for V1 instead of the 5879.  Using a paralleled V1 would allow you to use a 12V7, 12AY7 or 5751 which gives you different options for gain that a 5879 would not give.  In other words, it means you could dial in a cleaner tone using a 12AV7 and later switch to a 5751 for more gain.

Other than that ......................... I think the other components are needed especially the smoothing caps and enhance caps.

With respect, Tubenit

[PRR]

> a spec of 8W @ 100Hz. lo-freq down to 50Hz @ 4W seem doable

A strict interpretation for half frequency gives one-half Voltage, one-quarter Power, at similar distortion.

Since as you say guitar does not go below 82Hz (or if it does, it's funky), and considerable distortion may be tolerated in the bottom octave, I'm not worried.

OTOH, the little "universal" Hammonds are useful at various impedance and windings, which give various performances. It'll make your sick radio play again; whether it works good for guitar may require experimentation.

I don't think it is a great idea to build an amp around a specific OT (unless it is super-wonderful). The OT is not a real large part of the overall build.

[DummyLoad]

I don't think it is a great idea to build an amp around a specific OT (unless it is super-wonderful).

when it's all that's available, that's what you use. i doubt this modern stuff is not any worse than the penny pinching stuff that hit the streets in the sixties and seventies. and seriously doubt that very little, if any output iron was "tailor made" for the low watt "student" guitar amps. it's likely most did what we do today - try something already made or copy - order enough, you get your own OEM stamp and number.

--DL

[drgonzonm]

Just a poke HBP,  some of us amp users play low, 40Hz give or take on a standard bass, or 30 Hz if we play with a B0, five string.  82 Hz, is just tinny to some of us

[fuzz]

Hi,

I bump my thread to say that I'm still thinking about this . The thing is I want to use also a PT I've in stock and , this time, it is limited on the heater current (only 1,5A)

the EL95 is perfect choice , 200mA x 2 the rest for the preamp section But there're rare and 7 pins sockets .

also I've to find a small chassis and a headshell 

love making amps but may become a bit hard to do !   

i think I'll take one of the DummyLoad's list and see if I can get them cheap on ebay .

also , I've idea to put a bypass cap/trimmer + 1R to each cathode to set perfectly the bias but maybe it's overkill .