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Old 8th December 2019, 05:48 PM
grid leak grid leak is offline
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Location: Cleethorpes
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Default Ecf80 heater supplies kel 84

A few years ago I tried the DC heater supply mod listed in the upgrades and tweaks section of the forum. It was not completely successful, the voltages were not very stable, so I reluctantly retuned to the original arangement.
Forward on a few years, I decided to take another look at this subject. Having noticed a power supply unit that would work with 6.3 ac to 6.3 dc that wasn't too expensive, I decided to have another go! The Tentlabs Tube Heater Supply was duly fitted in the chasis of my Kel 84. There is enough space between the mains and output transformer, it sits on 4 stand offs with self adhesive strips supplied. The bridge rectifier needs to be removed and 0.6mm single stand wire for connection to input and output. The DC is applied to the terminal pins directly supplying the ECF80 valves. Ensure that polarity is maintained.
When fired up the voltage can be adjusted with a trimmer in the unit. The improvements you may notice are outlined in the Upgrades and tweaks section. I have found it has improved my more humble versions of the ECF80 valves the most. The Telefunken E80 CF that takes top spot was, however , still most favoured.
ECF80 valves are prone to microphony we are told, so any improvement in DC supply noise and hum seems to make quite a difference!
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Old 8th December 2019, 05:59 PM
Phil Y's Avatar
Phil Y Phil Y is offline
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Default Re: Ecf80 heater supplies kel 84

Strange that you could not get the normal mod to work as many, including myself have fitted it with no problems and found the sound improved. Glad to hear that this approach worked for you.

Phil.
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Old 9th December 2019, 10:06 AM
bob orbell bob orbell is offline
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Default Re: Ecf80 heater supplies kel 84

Ditto. Bob
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Old 9th December 2019, 07:33 PM
grid leak grid leak is offline
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Default Re: Ecf80 heater supplies kel 84

My WAD KEL84 does have some issues with the tracks on the cicuit board, this may well have contributed to the problem. Bypassing and hard wiring components has resolved all of the damaged tracks so far. The amp has been in almost constant use for 15 years and includes some mods and tweaks from the forum. The ECF80 heater supply mod is the only one which did not quite succeed!
It is difficult to produce low ripple dc at 6.3v from 6.3ac. The tentlabs module claims to reduce hum and noise to micro volts. It was easier to fit than expected, so I thought it may be of interest to any members who have considered upgrading the heater supply in their amps as an alternative option.
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Old 10th December 2019, 08:45 AM
bob orbell bob orbell is offline
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Default Re: Ecf80 heater supplies kel 84

A better idea would be a regulated supply, but you also need about 9 volts AC, doubt you would hear any difference though. Bob
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Old 10th December 2019, 11:40 AM
grid leak grid leak is offline
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Default Re: Ecf80 heater supplies kel 84

Just checked the Tentlabs website . The valve heater module does include a regulator along with Schottky diodes , 2 X 6800 uf caps and a power transistor. This seems to make their claim of ultra low ripple current credible at least!
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Old 10th December 2019, 04:55 PM
bob orbell bob orbell is offline
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Default Re: Ecf80 heater supplies kel 84

Put the supply on a scope, it should be a straight line, this is why I have mentioned HT regulators. Bob
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