Ecl86 power amp

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Bieworm
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Ecl86 power amp

Post by Bieworm »

People around here have any schematics for 18W amps with ECL86 power tubes and PI?
Which transformers and B+ voltages are ideal?
Geoff.. didn't you do this stuff in the past? And didn't you VVR the sh*'t out of it?
I'm thinking about doing a small tremolo tmb like that..
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Re: Ecl86 power amp

Post by geoff 1965 »

Yeah I used the trinity plexi 18W values in the phase & power section,i’ll take some voltage measurements for you,I think the PT has a secondary HT of 260-0-260 loaded.
Check out the Marshall popular and wem in the downloads but they don’t have 18W values.
here's the bogen 13W ecl86 phase & power section schematic,note the 18W values
bogen_schem2.jpg
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Re: Ecl86 power amp

Post by geoff 1965 »

Bieworm the loaded HT of my PT is 250-0-250 and my plate voltages are closer to 300 a bit more than the Bogen,for output transformers 18W will work but i’ve just fitted a Hammond 1750EP which is 15W and paper winding with 8K5 primary,el84’s in push pull is 8K and ecl86’s are 9K primary so that’s right in between. Tubetown are giving a good price on the hammond about €34 in the UK the cheapest I found was £55.
Will the tremolo TMB preamp work on the lower B+?
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Re: Ecl86 power amp

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geoff 1965 wrote:
Wed 11/03/21 11:06 am
Bieworm the loaded HT of my PT is 250-0-250 and my plate voltages are closer to 300 a bit more than the Bogen,for output transformers 18W will work but i’ve just fitted a Hammond 1750EP which is 15W and paper winding with 8K5 primary,el84’s in push pull is 8K and ecl86’s are 9K primary so that’s right in between. Tubetown are giving a good price on the hammond about €34 in the UK the cheapest I found was £55.
Will the tremolo TMB preamp work on the lower B+?
It might work with those voltages. It will sound different maybe, and the trem is a mystery for now.
Is ut a problem if I use mismatched ECL86 tubes? I have a NOS mullard, but I'll have to source another one... these are very expensive..OMG!
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Re: Ecl86 power amp

Post by geoff 1965 »

Here’s the reason I swapped that linear hi-fi output transformer,the resistance of the CT to plates were virtually the same,ideal for a hi-fi but not a guitar amp.the 1750EP has a resistance of 176R on one half and 237R on the other which even if you used perfectly balanced tubes you will have an imbalance in dissipation i.e. both plates have 285V to cathode but there is a difference of 1 volt in the voltage drop between the 2 resistances resulting in dissipation of 6.5W in one tube and 7.4 in the other with a closely matched pair.
The ecc83 halves of the tubes being a good match counts as they are used for the phase inverter “same as using a balanced ecc83” so I would think your better off with a matched pair.
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Re: Ecl86 power amp

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geoff 1965 wrote:
Wed 11/03/21 4:51 pm
Here’s the reason I swapped that linear hi-fi output transformer,the resistance of the CT to plates were virtually the same,ideal for a hi-fi but not a guitar amp.the 1750EP has a resistance of 176R on one half and 237R on the other which even if you used perfectly balanced tubes you will have an imbalance in dissipation i.e. both plates have 285V to cathode but there is a difference of 1 volt in the voltage drop between the 2 resistances resulting in dissipation of 6.5W in one tube and 7.4 in the other with a closely matched pair.
The ecc83 halves of the tubes being a good match counts as they are used for the phase inverter “same as using a balanced ecc83” so I would think your better off with a matched pair.
In that case it might be cheaper to add a dedicated 12ax7 for the PI and not use that part of the ecl86. And then buy a single ecl86.. or am I being too cheap?😃
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Re: Ecl86 power amp

Post by geoff 1965 »

Come on Bieworm! Just bite the bullet and buy a pair.
Sell a couple of those juicy telefunken el34’s!
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Re: Ecl86 power amp

Post by Bieworm »

I will try to source some. In the meantime I'm going to build me some blasphemic amp.. a guilty pleasure.. a 5F4 with 6G16 power tube bias vary trem. A deliciously rancid flubby amp😉
Last edited by Bieworm on Sat 11/06/21 4:28 am, edited 1 time in total.
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Re: Ecl86 power amp

Post by geoff 1965 »

try an ebay "european" search which will include france and holland etc.
the philip's branded tubes will be mullards anyway,there is still some NOS tubes floating around.
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Re: Ecl86 power amp

Post by zaphod_phil »

Bieworm wrote:
Wed 11/03/21 3:31 pm
geoff 1965 wrote:
Wed 11/03/21 11:06 am
Bieworm the loaded HT of my PT is 250-0-250 and my plate voltages are closer to 300 a bit more than the Bogen,for output transformers 18W will work but i’ve just fitted a Hammond 1750EP which is 15W and paper winding with 8K5 primary,el84’s in push pull is 8K and ecl86’s are 9K primary so that’s right in between. Tubetown are giving a good price on the hammond about €34 in the UK the cheapest I found was £55.
Will the tremolo TMB preamp work on the lower B+?
It might work with those voltages. It will sound different maybe, and the trem is a mystery for now.
Is it a problem if I use mismatched ECL86 tubes? I have a NOS mullard, but I'll have to source another one... these are very expensive..OMG!
I've said it many times that some mismatch will make your amp sound better, due to the increased even-order harmonics. Closely-matched valves and well-balanced PIs are really only recommended for Hi-Fi, not guitar amps.

I bought some used Mullard ECL86s on EvilBay from a guy in Australia. They weren't matched and the amp sounds fabulous :D
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