Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dunner84 on January 08, 2019, 07:10:32 pm
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New build time... I just did an inventory of all the spare parts I have been collecting, and I want to put my AO43 chassis to use. It is going to be a Dumble inspired build which translates to an ODS preamp (haven't decided which yet), and I really like the idea of a diode rec, tightly filtered, cathode biased, el84 power section. I have done some reading through previous ao43 builds, and it seems the transformer is a bit hot for el84s. Mine measures 315-0-315 unloaded. With a solidstate rectifier what kind of plate voltage would I expect?
I have a PT from an S6 organ that is 290-0-290 on paper, but measures 325-0-325 unloaded.. I have a wack of 350-0-350 PTs which are all probably too much, and one from a viking radio that measures 290-0-290. I have little experience with el84 amps, so I am not really sure what they will tolerate...
One other question for anyone with AO43 experience. Ch301 I believe is a 14H choke, but it seems a bit on the small side. I have a rather large choke that measures around 160Ohms, but I don't have any other info. It looks a lot like a Baldwin choke I have used in the past, and even has the B512 prefix, but the suffix doesn't turn up anything on the interweb.. I also don't have access to a sig gen or O-scope right now to determine the inductance. That being said, is the smaller Hammond choke usable for a build like this?
I am also not set on el84.. I will go with 6v6 if I have to, but I would really like the idea of el84s...
Concurrently, I will be building another Masco ME-18, but I will start another thread for it.
Any input would be greatly appreciated
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I would NOT recommend EL84's with a D-inspired preamp. I think you may end up with a harsh sounding amp,IMO.
Layout is super important in the D-inspired amps.
Most dumblish inspired amps get their OD from the preamp. Most EL84 amps that I know of get much of their OD from the power amp & EL84 tubes themselves. I heard a sound clip from a forum members years ago that combined those dynamics & I did not care for the tone. It did not sound dumblish to me. This was an experienced builder with lots of success in other amp designs.
I think you "should" build what you want, just offering food for thought.
It sure would be easier to offer thoughts IF you had posted a schematic.
With respect, Tubenit
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I can totally appreciate that. Some of my favorite Kingsley amps are dumble inspired, el84 amps though, and I have the itch to try.
For me, this is a hobby, and each build is a new learning experience. If I have the right iron for el84, I will go that direction, and if it doesn't sound right, it's not a big deal for me to mod the circuit, and chassis to go 6v6.
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here's an el84 based amp for study.
I like 84's, they drive easy, usually work well together, old ones you wanna keep plate reasonably close to 300vdc, modern ones I believe get abused to 400vdc a lot.
take your time, enjoy the challenge
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Some of my favorite Kingsley amps are dumble inspired, el84 amps though
I've been very impressed with the videos I've seen of the Kingsley amps. However, I am not aware of a dumble inspired one that uses EL84's?
Which one are you referring to? http://kingsleyamplifiers.com/products/amps/61/
I see some that are EL84 amps but nothing referencing those as dumble inspired?
I noticed that the HiWatt has 47k resistors to ground after the phase invertor. Perhaps that idea would work with a d-inspired EL84 amp?
With respect, Tubenit