Amp with one tube

[Leevi]

Does anyone have experience in ECL82 based amp?
http://nmwilliam.tripod.com/ecl82.html


Would it be enough for guitar?


http://www.drtube.com/datasheets/ecl82-philips1969.pdf


I'm planning to apply it with battery by using inverter.


/Leevi

[VMS]

Here is similar circuit:

http://www.lh-electric.net/projects/tiny3w.html

It says input sensitivity 0.3V, so you might need a boost pedal in front of it.

[HotBluePlates]

Or add a single-triode (such as 6AV6, 6AT6 or 6C4) in front of the existing circuit.

[Leevi]

Reason why I was planning to use ECL82 was the relative low heater current 0.78A.
However I noticed that by using 12AX7 + 6V6 the Ih is even less = 0.75A so why not to use a combination of those.
with a 6V/4000mAh battery you can in theory play some hours with one charge.


/Leevi

[mresistor]

cool and interesting Leevi


check this out   an se stereo amp 


https://youtu.be/SdIPugdnNIk

[Leevi]

Thanks for the link mresistor
It seems that ECL82 has been used in DIY stereo amplifiers.
By putting a line level signal in one tube can manage one channel.


/Leevi

[HotBluePlates]

Reason why I was planning to use ECL82 was the relative low heater current 0.78A.
However I noticed that by using 12AX7 + 6V6 the Ih is even less = 0.75A so why not to use a combination of those.
with a 6V/4000mAh battery you can in theory play some hours with one charge.

Yes but:

... I'm planning to apply it with battery by using inverter.

What impact will 35-45mA supplied by the inverter have on battery life? Check my math, as I haven't tinkered with inverters. If you need ~250vdc, that implies an inverted a.c. output of 250v/1.414 = ~177vac. If your homemade inverter uses a transformer to step-up the inverted 6.3vac, then the voltage ratio is 177v/6.3v = 28:1. The current ratio is the inverse of this, so for 45mA drawn in the B+ circuit we need 45mA * 28 = 1.26A drawn through the inverter from the battery plus whatever losses there are in the inverter's transistors & resistors.

Total draw looks like 1.26A + 0.75A = ~2A or a bit more.

Battery life could be lengthened a bit by reducing the current draw using a 12.6-0-12.6 transformer in the inverter, but the 12v rechargeable battery is perhaps twice as expensive as the 6.3v battery. Chargers are also somewhat expensive, relative to replacing all this with a regular PT.

But I don't know if you already have the rechargeable batteries & inverter, or if operation away from any outlet is an important consideration. If the latter is true, perhaps look into the series of tubes designed to run from batteries (but not the car battery/alternator, like the 6V6 & 12AX7).

[jojokeo]

Does anyone have experience in ECL82 based amp?

Would it be enough for guitar?

About 3 - 3.5 watts with a single tube (less than a Champ in power output), closer to 10w in pushpull. Are you making a guitar amp or a home stereo?

[kagliostro]

Ciao Risto

If you want an LND150 gain stage preceding the triode can be added

this way you can follow the GA-5T 61 Skylark schematic omitting the vibrato





Franco

[Paul1453]

This might be something to consider.

Supposed to be able to supply @200mA

[vibrolax]

This might be something to consider.

Supposed to be able to supply @200mA

According to the following link, this converter is rated for 40W continuous output, 70W peak.
So the current will be considerably less than 200 mA at typical plate voltages. For example 40W / 300V = 130 mA.
Assuming ~80% efficiency (specs claim up to 88%, but that depends on the input and output voltages), say 100 mA.

http://www.ebay.com/itm/DC-DC-45-390V-110v-220v-Boost-Buck-Converter-constant-current-power-supply-12v-/131537920919
I'm tempted to order one, to be powered by a laptop power supply.

[jojokeo]

"I'm tempted to order one, to be powered by a laptop power supply.,"

Why? Novelty or necessity?

[mresistor]

Does anyone have experience in ECL82 based amp?

Would it be enough for guitar?

About 3 - 3.5 watts with a single tube (less than a Champ in power output), closer to 10w in pushpull. Are you making a guitar amp or a home stereo?

He's interested in guitar amp. My link was just to show that the 6BM8 can be very clean. As well it has less footprint over a 12AX7/6V6 combo.

[Paul1453]

This might be something to consider.

Supposed to be able to supply @200mA

According to the following link, this converter is rated for 40W continuous output, 70W peak.
So the current will be considerably less than 200 mA at typical plate voltages. For example 40W / 300V = 130 mA.
Assuming ~80% efficiency (specs claim up to 88%, but that depends on the input and output voltages), say 100 mA.

http://www.ebay.com/itm/DC-DC-45-390V-110v-220v-Boost-Buck-Converter-constant-current-power-supply-12v-/131537920919
I'm tempted to order one, to be powered by a laptop power supply.

I only played with it for a short time,
but it did seem to have the current capacity to power a PP EL84 Hoffman Stout with the 19V input. 

[vibrolax]

"I'm tempted to order one, to be powered by a laptop power supply.,"

Why? Novelty or necessity?

Novelty.  I'm wondering how these inexpensive boost converters would perform in a PP EL84 or 6V6 amp.
I'd probably use a separate buck converter for the filaments, possibly followed by a linear regulator.

[Paul1453]

I can often get these laptop bricks with a broken output connector out of the trash for free.   

On a different forum, someone mentioned that with 19V I should be able to power the heaters of 3 12AX7 connected in series.
I still need to figure out how to power the heaters of the output tubes with it.

I used the 6VAC from my bench supply, and the HV B+ from this board in my short test.

If I can figure out how to power the other heaters from the laptop brick,
I'd have a full PS for under $9. 

Then the size and weight of this option is quite favorable, for a little amp. 

[vibrolax]

I can often get these laptop bricks with a broken output connector out of the trash for free.   

On a different forum, someone mentioned that with 19V I should be able to power the heaters of 3 12AX7 connected in series.
I still need to figure out how to power the heaters of the output tubes with it.

I used the 6VAC from my bench supply, and the HV B+ from this board in my short test.

If I can figure out how to power the other heaters from the laptop brick,
I'd have a full PS for under $9. 

Then the size and weight of this option is quite favorable, for a little amp. 

Use a separate buck converter to give 6.3 vdc from the 19v brick.  A boost converter for the b+, a buck converter for the filaments

[Leevi]

Thank you for very informative responses.

What impact will 35-45mA supplied by the inverter have on battery life? Check my math, as I haven't tinkered with inverters. If you need ~250vdc, that implies an inverted a.c. output of 250v/1.414 = ~177vac. If your homemade inverter uses a transformer to step-up the inverted 6.3vac, then the voltage ratio is 177v/6.3v = 28:1. The current ratio is the inverse of this, so for 45mA drawn in the B+ circuit we need 45mA * 28 = 1.26A drawn through the inverter from the battery plus whatever losses there are in the inverter's transistors & resistors.Total draw looks like 1.26A + 0.75A = ~2A or a bit more.

The total current consumption is of course a thing I have to take into account.
12V battery is a good choice especially if there are two tubes and the heaters can be serial connected.
The price is not an issue if the result is remarkable better.


My idea is to build a home made inverter and I'm thinking how much hum that will cause?


Of course the amp shall include a regulated charger circuit and inputs for AC and 12V (eg. solar cell).


/Leevi

[PRR]

> with inverters. If you need ~250vdc, that implies an inverted a.c. output of 250v/1.414 = ~177vac.

Inverters usually run square wave. The 1.414 does not apply.

"No free lunch" still applies. The DC out is always less than the DC in. High frequency designs can exceed 90% efficiency. Bodge-ups may not reach 50% eff.

_IF_ you work one tube at the full 7W Pdiss (say 8W with driver and bias), at 6V battery it is over 1.33 Amps. Say 1.5A until the inverter is perfected.

Plus 4.6W or 0.78A in heat. Round to 2 Amps??

> with a 6V/4000mAh battery

So 2 hours play-time to FLAT battery. Most batts do not like being run dead-flat. Lead-acid (motocycle, alarm) batts lose a lot of life every time you run them right down. LiOn etc have more complicated discharge limits.

6V6 is not only more bang per heater watt, it looks bigger-better-badder. And I can't think why bother with portable tubes unless it adds to your busker-appeal? "Daddy! That guy has bottles on his box! Slip him an extra buck!"

[Leevi]

Inverters usually run square wave. The 1.414 does not apply.

Yes, 555 timer circuit is one which has been used. You can easily set the frequency as well.
How does the transformer work if you increase the frequency?

So 2 hours play-time to FLAT battery.

The battery will be a transferable unit that can any time be replaced with a bigger one
or power the amp via 12V input e.g. from a car.
Let's say with a motorbike battery you can play several hours on the street.


/Leevi

[tubeswell]

Another amp for a (ECL86) single audio tube (and rectifier)


http://www.r-type.org/articles/art-003g.htm

[kagliostro]

On the two tube choice there is one other option to have a lower heater consumption

instead of 5F1 with 12AX7 + 6V6

12AX7 - 6.3V @ 300mA

6V6 - 6.3V @ 450mA

total 750mA

a 5C1 with EF86 + 6V6

EF86 - 6.3V @ 200mA

6V6 - 6.3V @ 450mA

total 650mA

or 6AK5 + 6V6

6AK5 6.3V @ 175mA

6V6 - 6.3V @ 450mA

total 625mA

or 5879 + 6V6

5879 - 6.3V @ 150mA

6V6 - 6.3V @ 450mA

total 600mA

with 5879 + 6V6 respect the 12AX7 + 6V6 you can save 150mA

Franco

[Leevi]

Thanks Franco,


It seems to be several ways to minimize the heater current.


/Leevi

[Paul1453]

That little board I posted would work with your 12V car or motorbike battery!

Cheap, easy, and lighter for a small portable tube amp.   

[Leevi]

That little board I posted would work with your 12V car or motorbike battery!

Yes, the specs look promising. Have you tried it?


Thanks
/Leevi

[Paul1453]

Not with 12VDC.

I experimented a little on my breadboard with my bench PS providing 6.3VAC for the heaters,
and this little board powered by a Dell brick at 19VDC.

That worked to power the HV circuit of the PP EL84 Hoffman Stout.

You could have a 12VDC power input that powered the heaters and this board.

I think that could work. 

It's less than $9 delivered to try it out yourself. 

[shooter]

I'm planning to apply it with battery by using inverter.

you might wanna *test* your invertor next to a working amp, I've found they can be great noise generators.   

[Paul1453]

I'm planning to apply it with battery by using inverter.

you might wanna *test* your invertor next to a working amp, I've found they can be great noise generators.

I was thinking the same thing.   

The computer UPS's I've used buzzed like a bee when they went to battery operation.

Also the little inverters I've used in a vehicle seemed OK to power a laptop,
but not so much for audio or video appliances. 

[vibrolax]

The computer UPS's I've used buzzed like a bee when they went to battery operation.

That's because the UPS inverter is outputting 120 VAC @ 60 Hz, where the 60 Hz is only a sine wave if you bought a more expensive sine wave inverter.  In the cheap UPS's, the output is a square-ish wave, or a "modified sine wave" with all kinds of interesting harmonics.

The DC-DC inverter referenced previously claimed to have a switching frequency of 75 kHz.  That's not necessarily going to buzz, though it might, depending on the inverter circuit topology.   There can be quiet SMPS's, but I'm not betting that these simple modules are going to fit in that category.  It seems like an interesting $10 experiment.

[Leevi]

The hum/noise is definitely an issue with cheap square wave inverters.


The DC-DC inverter might be worth for trying because of its low price.


/Leevi

[Leevi]

I got the first draft of the battery amp wired. I used the DC-DC converter that Paul1453 recommended.
Have to say that it is an excellent product. It keeps the set voltage and doesn't cause hum at all.


Some specs:


Batteries 10 x 1.2V NiCd cells tot. 4000mAh
PT: 230V/14V 3.65A, the current must be high enough
LM317 in charger circuit
Amp part 5F2-A without tube rectifier
With 250V B+ and 11.5V (470R) cathode the total current consumtion ~1A


/Leevi

[kagliostro]

Some specs:


Batteries 10 x 1.2V NiCd cells tot. 4000mAhPT: 230V/14V 3.65A, the current must be high enoughLM317 in charger circuitAmp part 5F2-A without tube rectifierWith 250V B+ and 11.5V (470R) cathode the total current consumtion ~1A

Schematic of the 5F2-A but .... using which tubes ?

Franco

[Leevi]

Schematic of the 5F2-A but .... using which tubes ?

TAD 6V6
http://www.tubeampdoctor.com/de/shop_TAD_Premium_Tubes_TAD_Power_Tubes_SELECTED/6V6GT_Summer_Of_69_Special_TAD_PREMIUM_Matched_3269


JJ 12AX7


/Leevi

[kagliostro]

Ah, OK, so you followed the use of the 5F2-A traditional tubes


Franco