Lunchbox ECL86

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wmwelch55
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Re: Lunchbox ECL86

Post by wmwelch55 »

In my experience, the MOSFET needs a heatsink. Mine gets pretty hot.
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

Yeah it has a 2mm silicone heat transfer pad underneath the mosfet and the fibre board is 14mm thick.i will monitor it and see if there is a problem.taking some time out to learn the basics of using my oscilloscope now.
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zaphod_phil
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Re: Lunchbox ECL86

Post by zaphod_phil »

geoff 1965 wrote:
Wed 06/16/21 12:05 pm
Yeah it has a 2mm silicone heat transfer pad underneath the mosfet and the fibre board is 14mm thick.i will monitor it and see if there is a problem.taking some time out to learn the basics of using my oscilloscope now.
The MOSFET will need to be mounted on a metal surface, with the silicone pad, to transfer its heat away, not the circuit board.
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

Okay will do,might need to alter the board to suit.i’ve also sourced some FQA9N90 mosfets which are a lot closer in spec to the NTE2377 on the schematic.
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musicheals
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Re: Lunchbox ECL86

Post by musicheals »

Why not place a smaller heat sink between the mosfet and the fibre board. For better heat transfer you could mount it without an isolation pad, if the heat sink is not connected with the chassis....

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Re: Lunchbox ECL86

Post by JMPGuitars »

Or mount the MOSFET vertically instead of horizontally, and then you have a lot of heatsink options without needing to worry much about the board.
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

Update on the little ecl86 plexi,i’ve made a small vvr board and now the mosfet is bolted to the chassis and is working good.
Also replaced that linear hi-fi output transformer with a Hammond 1750EP which is 15W and 8K5 primary and 8 ohm secondary “I can test now with my favourite eminence speaker” should be more suitable now with a guitar amp OT.
I bypassed the effect loop triode for now until i’ve finished tweaking the amp then I can concentrate on that last.
884D3BD1-0DBC-49CF-BCF5-1816EC678FA8.jpeg
BECAF514-9EAB-4568-B563-DA85D42DEDA0.jpeg
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

7779D2AB-013F-4039-A931-8FDADF8455FA.jpeg
Fitted the tinted Perspex front and happy with it,also fitted a 5ohm 6amp thermistor just for the soft start protection for the mosfet,zener etc in the vvr section.
Decided to go passive series with the effects loop,it works for me and there is no resistors/capacitors involved,I did’nt want to go through the amp setting gain & tone then have to attenuate it after the buffer triode into the phase inverter.so I have just used the extra triode to parallel V1 and going to experiment with that.
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

VVR gremlins again!
when on full or minimum voltage the volume is fine,however if i sweep from full power down i'm getting massive noise,not sure if it's the mosfet but i changed back to the "hall's" layout except the screens tap which i have in my capacitor tester and has been no problem.the 32/32 can cap is brand new so i don't think filtering is the cause. here's my layout and also the halls version.
VVR.jpg
hall_vvr.jpg
good news is i'm getting some cracking tone/breakup with this plexi circuit and the ecl86's
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

134DA110-1AA9-42ED-B205-09A330D4C306.jpeg
Mosfet number 3! gone through all the components on the vvr board and fitted another new mosfet and all values are correct.the one thing coming to mind is the potentiometer,the volume was good on max and good on minimum with no noise,the problem was when sweeping up or down so maybe the carbon track was damaged when the first mosfet played up? this has me stumped but i’m determined to sort it out!
Also now the B+ has settled with all the tubes biased it’s a little too high,plate voltage diode rectified is 312V and 298V tube rectified,I don’t want to push the ecl’s over 300 so i’m going to drop the B+ 10 volts with a 5W zener.
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

2 little buddy’s have just arrived! one for the plexi ecl86 and one for the 18W amp.
D4E10765-4CEC-4D88-B512-F0BD8936971A.jpeg
C654CA01-0301-4DDC-88CF-7C5CB75F16D9.jpeg
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Re: Lunchbox ECL86

Post by Bieworm »

geoff 1965 wrote:
Fri 11/26/21 8:59 am
2 little buddy’s have just arrived! one for the plexi ecl86 and one for the 18W amp.
D4E10765-4CEC-4D88-B512-F0BD8936971A.jpeg
C654CA01-0301-4DDC-88CF-7C5CB75F16D9.jpeg
Niiiiiiice!!!
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zaphod_phil
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Re: Lunchbox ECL86

Post by zaphod_phil »

Bieworm wrote:
Fri 11/26/21 12:44 pm
geoff 1965 wrote:
Fri 11/26/21 8:59 am
2 little buddy’s have just arrived! one for the plexi ecl86 and one for the 18W amp.
D4E10765-4CEC-4D88-B512-F0BD8936971A.jpeg
C654CA01-0301-4DDC-88CF-7C5CB75F16D9.jpeg
Niiiiiiice!!!
Those two "Made in England" G12H-30s will sound big and solid! Hardly "little buddies" :lol:
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

Yeah ZP!
They were in a solid state carlsbro amp that was spares/repairs,date codes are October1971 and October1972,50 years old and look at the cones they are mint,these have been looked after.
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