Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: shortfuse on March 15, 2013, 10:50:28 pm
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Has anyone built this amp or know of any known issues with this layout? I have not built an amp in over a year now and I have the itch, chassis, 70% of the parts & Iron to build this one. I like it because it is different and not something I have used before.
Comments suggestions?
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I finished one couple of weeks ago, its a great amp. Only change I made to the physical layout (apart from a few parts substitutions) was to use shielded wire for the more sensitive wires. And also placed the 470k grid resistor on the 2nd gain stage of the tmb side on the actual tube socket. There's a thread somewhere below with my build in it.
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Thank you I read through your post and project some good info there.
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Should I use a choke instead of the 1K5 5W Resistor? What would the end result difference be? And if I were to use a choke what would be the correct "H" value to use?
I see Marshall uses 10h in the 1974x, but Dougs Stout uses a 4h. :dontknow: This is why I just got the books I did.
There was a great thread on chokes and Henry's a year or so ago and I cant seem to find it. Could someone please give me that link?
Also where can I get the EF 6 position Switch? Did not see it in Dougs Store I think Weber is the only place I found one.
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A choke will stiffen the power supply. I find the difference between a resistor and a choke is basically to calm the amp down a little, it takes away some of the Marshall "bark" and replaces it with some Vox like consistency - the overdrive tone will be a lot more regular and even.
If you check out Mercury Magnetics they have a 10H choke (About the same value that was used in the vox ac15) or they have a cool adjustable henry choke - so you can select your favourite value.
Using a choke won't make the tone of the amp "better" but it will change it and for me it moves it away from the raw Marshall tone, I prefer the resistor.
I'm in Europe and I source my parts from banzai, rapid, mouser, tube amp doctor and Ingo gorges transformers. I get my cabs from ampmaker's Chris... For the 6 position switch you can get the 12 position 1 pole rotary switch and just use the lock nut they come with to lock it at 6 positions.
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Also where can I get the EF 6 position Switch?
Radio Shack has it. Actually, their's is a 2 pole, 6 position. Get the one with the 'make before break' action and you won't have to put any resistors on the switch.
EDIT... AES has the switch also.
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Also where can I get the EF 6 position Switch?
Radio Shack has it. Actually, their's is a 2 pole, 6 position. Get the one with the 'make before break' action and you won't have to put any resistors on the switch.
EDIT... AES has the switch also.
That's good advice, soldering those damn "anti-pop" resistors on the switch is a real pain.
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You don't need the switch unless you're going for a complete copy/clone. All those settings are useless. You only need a few which can be put on a simple switch similar to a guitar having all of the out of phase options etc. They're almost never used after the initial newness & gimmickery wears off. There's a lot more "worth while" things giving a much better bang for the buck there on an amp like that.
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Bluemeany
Thank you for the info I will go with the resistor to start with and maybe try out a choke later.
Steve
Great suggestion less work for me thank you. I take it the switch shown in the layout is a "break before make" type.
Joe
There's a lot more "worth while" things giving a much better bang for the buck there on an amp like that.
Cough some up I am in the putting the remainder of the parts list together mode. Open to any and all suggestions. I have not built and amp for over a year and I have the itch and most of the parts for this one.
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Loose the space hogging 6-way and put a pot in there to control the gain of the tube properly. Use a switch for a couple different coupling cap options using a .02, .01. and either a .005 or .002 in there - that's plenty. You can mimick the 12ax7 gain & response using the EF86 in triode or morph mode thereby eliminating that aspect of the circuit & using those controls for things like more cascading or a CF stage, and incorporating a tone stack bypass which really sounds good w/ an EF86. Add in some switchable feedback or presence control. A bypass boost for the CF stage. VVR on the PA/PI...If you're at the part ordering stage and want to get your build on then you're not ready for any of this stuff because it'll change the whole design and layout. Maybe best to make this one and then on the next one you can go bigger, better, farther?
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I have the 36 watt model for one of my own personal arsenal.
It's a pretty cool amp.
I like the EF86 side.
Too bad I can't find decent EF86 tubes.I run into microphonic ones.
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I have the 36 watt model for one of my own personal arsenal.
It's a pretty cool amp.
I like the EF86 side.
Too bad I can't find decent EF86 tubes.I run into microphonic ones.
The tube amp doctor one I'm running is going well, it was expensive though.
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I've build up a pretty large stash over time and the newer ones aren't all that bad in comparrison. But even the best ones can get a little microphonic if run too hard and in a combo amp turned up high. Best to run them w/ a bit less gain, in a head, and in doing this I haven't had hardly any issues no matter how hard I drive them and high volume.
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check these out got some but havent tried yet http://www.ebay.com/itm/NOS-new-EF86-6267-Mesh-Plate-Vacuum-Tubes-7-each-/390553058657?pt=Vintage_Electronics_R2&hash=item5aeec6bd61thse (http://www.ebay.com/itm/NOS-new-EF86-6267-Mesh-Plate-Vacuum-Tubes-7-each-/390553058657?pt=Vintage_Electronics_R2&hash=item5aeec6bd61thse)
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I might give them a try.
I tried the JJ equivalent with no success.
Gave up.
I usually end up putting the head on the floor off the speaker cab.
Would love to find some decent tested and true new EF86s.
I'd build an entire amp off that preamp tube.
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http://www.banzaimusic.com/TAD-EF86-6267.html (http://www.banzaimusic.com/TAD-EF86-6267.html)
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I tried the JJ equivalent with no success.
What do you mean - microphonics issue?
Would love to find some decent tested and true new EF86s.
I'd build an entire amp off that preamp tube.
I think the ones that are tested only are done so by a tube tester but not "real world worthy". Maybe tested or used "under normal circumstances" but what is "normal"? Certainly not us!
Have you tried a 5879 (slightly less gain) or if you can try a 7-pin tube - the 6ak5 is the one. These were high freq tubes meant to be used in aircraft w/ high vibrations, at elevations, and built to work under high G-forces. Hell, they seem like they were made just for us!? Geezer & I have used these with good results. I haven't run a side by side comparrison w/ an EF86 but they sound really good to me.
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http://www.mcmaster.com/#o-rings/=lypbr1 (http://www.mcmaster.com/#o-rings/=lypbr1) measure the outer diameter of the ef86 . and order high temp SILICONE o-rings to dampen the microphonics.. maybe two rings per tube.
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http://www.banzaimusic.com/TAD-EF86-6267.html (http://www.banzaimusic.com/TAD-EF86-6267.html)
Notice that's the same tube, relabeled, for 4x the price as what Davidg posted.
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http://www.mcmaster.com/#o-rings/=lypbr1 (http://www.mcmaster.com/#o-rings/=lypbr1) measure the outer diameter of the ef86 . and order high temp SILICONE o-rings to dampen the microphonics.. maybe two rings per tube.
I haven't experienced ZERO benefit from these and/or special mounting socket tricks. The tube still suffers from vibrations either way. The circuit design needs to be adjusted and not using EF86's in a high powered combo amps is the best ticket. This isn't gospel just my experiences.
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... if you can try a 7-pin tube - the 6ak5 is the one. ... they sound really good to me.
The 6AK5's are that good, huh? Any preference of 6AK5/EF95 vs. 5654/6AK5W?
I actually have some old test gear that uses these, so I could stand to get some backups anyway. But if they're that good for guitar use, then...
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http://www.banzaimusic.com/TAD-EF86-6267.html (http://www.banzaimusic.com/TAD-EF86-6267.html)
Notice that's the same tube, relabeled, for 4x the price as what Davidg posted.
Indeed, but at least you know it's tested as good and can return it if you have problems. I might buy a couple of those and keep them in my back pocket for further projects - these ef86 tubes have quickly become my favourite preamp tube, they really are a rich, hormonically complex tube, well worth the trouble to find a good one!
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The 6AK5's are that good, huh? Any preference of 6AK5/EF95 vs. 5654/6AK5W?
Not sure there's much of a difference as I've used both but I think the 5654 is the ruggedized military version. Yes you should give it a go and see for yourself if you can.
I might buy a couple of those and keep them in my back pocket for further projects - these ef86 tubes have quickly become my favourite preamp tube, they really are a rich, hormonically complex tube, well worth the trouble to find a good one!
Been my fav for a number of years now and why I've always collected up a pretty good supply of 'em when I find the right ones at a good price.