Lunchbox ECL86

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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

09DED864-CAAD-47F6-82A7-9650CFB15935.jpeg
From the input Jack to pin2 of V1 is only 2 inches,so do I make a very short shielded cable or risk jumping the grid resistor across?
I found some Marshall plexi reference voltages to compare with the trinity,quite a bit of difference in plate voltages due to the cathode biasing I.e. the trinity has 820R/.68uf and the Marshall 2K7/.68uf I imagine there will be quite a difference in tone as well,will experiment with that one.already replaced the clean boost values with 820R on the V2 cathode.
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Re: Lunchbox ECL86

Post by JMPGuitars »

geoff 1965 wrote:
Wed 05/26/21 6:15 pm
or risk jumping the grid resistor across?
How is that a risk? Do you not trust your soldering skills? ;)
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Re: Lunchbox ECL86

Post by geoff 1965 »

risk as in the resistor leads acting like mini antenna's Josh,or am i being overly concerned there?
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Re: Lunchbox ECL86

Post by JMPGuitars »

geoff 1965 wrote:
Wed 05/26/21 8:13 pm
risk as in the resistor leads acting like mini antenna's Josh,or am i being overly concerned there?
Overly concerned. If they act as antennas, then consider doing something else. But 2 inches isn't likely long enough to hurt anything.
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

Okay i’ll try that,can do the same with the gain pot as well.
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Re: Lunchbox ECL86

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32E27E12-5AE4-4D63-AE41-6DAA3A3F6D94.jpeg
7C10E28F-8AB1-4365-B12C-4AD01447AF20.jpeg
All wiring done now except the couplers to the pots,just waiting for those,initial power up tonight then I can take some voltage measurements and adjust the B+ rail to suit.
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Re: Lunchbox ECL86

Post by TriodeLuvr »

Nice work! Are those 1/4" jacks on the rear panel carrying preamp signals? Grounding them to the chassis might be a concern.

Jack
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

Yes Jack it’s the FX loop and now you point that out the Hiwatt schematic shows no grounding of the loop,can easily cut the grounds if there is a problem.i want that signal wire from the treble pot shielded as it passes over the tag board,I could ground the wire at the pot side if needed.
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

initial startup good,no smoke or fireworks and zero on the bulb!
I was’nt exactly sure what plate voltages on the pentodes to expect but was looking between 275-300 to be happy.anyway look at the pics i’ve got 303 diode and 285 ez81 rectified with vvr on max.
6129F7BE-6CEF-45D6-A2A9-3A27125058B5.jpeg
D5D672D5-6B01-4667-BA7C-130EB338DECD.jpeg
Have to adjust the B+ rail now for the phase inverter and preamp and a thorough test of that vvr mosfet!
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Re: Lunchbox ECL86

Post by TriodeLuvr »

Good job, looks great!

Jack
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Re: Lunchbox ECL86

Post by JMPGuitars »

Agreed, it looks awesome. I want to hear it when you're done!
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Re: Lunchbox ECL86

Post by Bieworm »

Me too
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"THIS should be played at high volume..preferably in a residential area"

geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

Thanks for the comments lads,just made the base plate and the B+ rail voltages are done,waiting for the couplers then I can test with a speaker!
A2DE963B-C36A-4340-B4B1-6B5D3859D1EE.jpeg
48B6B311-364B-474C-A53D-162BF76071A7.jpeg
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

B16D0EFF-D545-49E2-B511-6045A7A4BFDB.jpeg
Wiring finally done! ungrounded the FX loop and i’ve used a A250K pot for the volume to start with the extra triode to buffer the effects.i used Teflon sleeving for the couplers & resistors.
The only 4 ohm speaker I have is this black star 12” 50W,not ideal but should be okay for testing.will post progress and full voltages.
708C8CC3-D986-4C4D-8949-45097262AA66.jpeg
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Re: Lunchbox ECL86

Post by geoff 1965 »

1EBA7B36-609B-4468-BAC8-72D979C286DC.jpeg
Just had a moment! I was taking voltage measurements and when I got to the second pentode plate the reading went off the scale so I immediately unplugged and checked the wiring for whiskers etc then I swapped the tubes around and the same thing happened.it was the volume pot on max and it was overloading the phase inverter,backed it off and everything was good so I have some attenuating to do there which I expected.going to rig the speaker up so I can hear when attenuating the signal and swap the 250K pot for a 100K.
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

Vvr problem!! just done a test of the voltage sweep on the vvr unit and this is what I got,minimum 31V,one third turn 1200V!!,two thirds turn 600V,maximum 312V. luckily all the tests i’ve done so far we’re on full 312V.
C5F5D870-E6CF-47E9-B0EC-078F89A7B102.jpeg
this is the vvr,the 100K goes to the pot wiper and the diode to the input lug with a 100K to ground from lug 3.
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Re: Lunchbox ECL86

Post by TriodeLuvr »

Well, it can't really be +1200V, can it? May be it's oscillating and fooling your meter.

Jack
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Re: Lunchbox ECL86

Post by Daviedawg »

Was it under load or isolated from the circuit when you tested?
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geoff 1965
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Re: Lunchbox ECL86

Post by geoff 1965 »

it was in circuit under load Dd,going to remove the valves and retest on both diode & ez81 rectifier and use both of my multimeters to see if it's an oscillation like Jack mentioned.very quickly as i don't want to damage anything i.e. OT or filter caps etc.
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Re: Lunchbox ECL86

Post by TriodeLuvr »

I think you need a scope for this. Or try it with your meter on an upper range of AC volts.

Jack
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