Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: LPJr on October 25, 2021, 11:36:11 pm
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Hi all, newbie here. I built a 5e3 kit as my first build and I love it. In my searching I found Hoffman and Robinette to be great resources! I decided on a 5f6-a as my next project since I can build a head and use my Super Reverb as a speaker cab...I’ve ordered up all of Hoffman’s parts list and a turret board, but I need to order transformers and they’re out of stock or super expensive. I have an old Super 60 I was trying to decide if I want to repair or part out and I see it has the 018343 output transformer...will that work as a drop in to Hoffman’s 5f6a layout?
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It will "work" but with different output and distortion. How close do you want to be?
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Well I saw in an old list it said to use 018343 for a 2,4,8 ohm output, is this have the right specs? I like the idea of output options, but is the 2 ohm only version going to have a different sound? I love the Super and Bassman 4x10 sound.. but if it can sound like that plugged into that configuration but I can have other options available especially if I make it a head...basically I love the ‘tweed’ sound of my Deluxe build and am hoping for a higher watt version. I’m committed to a 5f6a turret board and chassis at this point, and also ordered the Hoffman small parts list... how do you think the Fender OT would sound?
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Sorry meant to say it was on an old Hoffman parts list where it said use an 018343 for multiple output impedences, so I thought maybe I lucked out when I saw those numbers in the Fender OT...so is this interchangeable?
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here's a good read on OT, nothing on how to make them sound like (insert your favorite amp here) but the how they work part is good
Output Transformers Explained (aikenamps.com) (http://www.aikenamps.com/index.php/output-transformers-explained)
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Everything affects everything else. And intuitively, only drawing load current through 1/2 the secondary winding (as would be the case with the 2ohm tap for that OT) would seem non ideal and bound to affect the sound somehow.
But in reality it doesn’t seem to be an issue, amps don’t tend to measure or sound perceptibly any different according to the output tap used.
And a Super Reverb cab will probably sound different to a Tweed Bassman cab anyway.
So if that Super 60 was scrap, I’d have no qualms about using its OT for that project.
But that’s a valuable amp, is it really scrap?
If you aren’t interested in fixing it, as long as it looks in reasonable condition, it has intrinsic value even not working, so it’s almost certainly still worth selling it.
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2 4 8 16 are all 98% the same if the transformer was designed for that. Same frequency response. Not even a Watt difference of power output.
018343 is 6,600ΩCT. 5F6a is 4,000ΩCT if I recall correctly. That's enough difference of loading to be noticed. But if you are mostly concerned with using Available Parts (especially in the current shipping crunch) and not over concerned with the Super 60's value, then do it. I don't see why it has to be stripped though. The Super has a higher B+ which will suit the 018343 just fine, maybe a trace more power than a stock 5F6a. The Super has a lot of fancy switching and Blackface tone controls, and I assume a PCB, so strip that much and fix it right.
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You can get the Hammond 290DX for $98 and the Hammond 1760K OT for $83 at Hawk Electronics. I don't consider that "super expensive". Large iron has large price.
As recommended above it is advisable to fix the Super 60 and sell it and use the money for your 5F6A build.
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Everything affects everything else. And intuitively, only drawing load current through 1/2 the secondary winding (as would be the case with the 2ohm tap for that OT) would seem non ideal and bound to affect the sound somehow.
But in reality it doesn’t seem to be an issue, amps don’t tend to measure or sound perceptibly any different according to the output tap used.
Interestingly, at least some people have found a difference with different OT taps. I always felt like I should want to use the 16 ohm tap on an OT so that I was using the "entire" secondary. But, listening to their sound samples below, I think I actually preferred the lower impedance taps.
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Thanks all- great answers. The Super 60 is a decent amp, I picked up for only $200 as is and it just quit on me, but I think it was just a tube failure and hopefully the internal fuse...thanks for all the great advice and I was having qualms about scrapping it...they are a Super pain to work on, everything on the bottom of a huge board with tube sockets hardwired to it....techs hate them I hear...if power tubes and a fuse fix it I’ll take your advice and sell it. Thanks again! Especially the tip on Hawk selling those Hammonds so reasonable (if they ever get back in stock)- I also don’t live far from Hyboer so maybe I’ll try contacting them direct...
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If they're out at Hawk then try Antique Electronics Supply - a couple of dollars more but good outfit to order from. https://www.tubesandmore.com/search/node/290DX?cats%5B0%5D=65
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Thanks guys- Hawk had 1 Hammond PT in stock, placed order for Hammond PT, OT and choke- $260 for all three...at least I know I’m getting quality and the right specs. Small parts arrived from Hoffman today.... so the Super 60 is for sale....lol
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Well just saved $50-
You can get the Hammond 290DX for $98 and the Hammond 1760K OT for $83 at Hawk
Thanks mresistor, I reviewed this and realized I had ordered the 290d2x instead of 290dx, and I’m assuming I want the lower plate voltage? Caught it in time and changed my order and it saved me $50 too! So please confirm for 5f6a the lower plate voltage is what I want?
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I think you'll be just fine with the 290DX.
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Ok guys need some more advice- I’ve got my Hoffman parts package, but I got the turret board from Tube Audio Supply, and it’s not for the Hoffman layout. It does match the RobRob layout, but there are some differences with the RobRob circuit and the Hoffman- for one Hoffman has 5 22/500 filter caps instead of 4, 10uf Bias filter caps instead of 8uf on RobR, and a few other resistor values are different. Can anyone chime in if these are significant differences or am an ok following the RobRob layout (with the exception of using Hoffman’s bias resistor values and trim pot, seems like a good idea) Especially can I just use 4 of the five doghouse caps or should I use all 5? TIA
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You know, Hoffman sells boards too. I predict you will have many more questions like this by using Hoffman's parts kit with someone else's board. Your build will go much smoother if you just buy the Hoffman board. IMO the bias improvements justify the board cost.
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Ok Sluckey I was contemplating that I think I’ll take your advice and order the Hoffman board. After searching around I really like the clean look of his layout, and the above the board wiring.
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Good idea. Now put Rob's documents in the round file.