Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Bieworm on September 21, 2020, 01:23:33 am
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Hi there!!
I am thinking about doing some sort of clone build of a Tone King Imperial. Does anybody have more information about the voltages on the B+ rail?
Is there more information available about the specs of the powerTx and the OTx ?
thanx!!
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" The Tone King Imperial was designed by Mark Bartel and is based on the Fender Deluxe Reverb design but with some notable tweaks."
https://valvetubeguitaramps.com/tone-king-imperial/
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I'll go for Fender Deluxe Reverb voltages:
https://robrobinette.com/How_The_AB763_Deluxe_Reverb_Works.htm
Transformers specs ; look at tubesandmore ;
https://www.tubesandmore.com/products/transformers_chokes?filters=Replacement%20Type%3DReplacements%20for%20Fender
Show us the schematic of the Tone King you want to built .
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" The Tone King Imperial was designed by Mark Bartel and is based on the Fender Deluxe Reverb design but with some notable tweaks."
https://valvetubeguitaramps.com/tone-king-imperial/
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I'll go for Fender Deluxe Reverb voltages:
https://robrobinette.com/How_The_AB763_Deluxe_Reverb_Works.htm
Transformers specs ; look at tubesandmore ;
https://www.tubesandmore.com/products/transformers_chokes?filters=Replacement%20Type%3DReplacements%20for%20Fender
Show us the schematic of the Tone King you want to built .
oh... haven't realised that. In that case I think I will be better off building a deluxe reverb and tweak from there. I will surely not do the optotrem, but go for the bias vary trem. Will only build it with the trem channel. Any known good ideas that will work to obtain a nicer overdrive than the standard DR? something less flubby...
The toneking has a very nice overdrive for that matter...
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For nice overdrive, I'll use good overdrive pedal.
I built a Deluxe Reverb amp from scratch, a great sounding amp
No Tone king schematic ?
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For nice overdrive, I'll use good overdrive pedal.
I built a Deluxe Reverb amp from scratch, a great sounding amp
No Tone king schematic ?
yes. here they are. but they are not entirely clear to me..the heater wiring for example..the tube numbering does not correspond with the schematic + pin numbering is not right either IMHO
And I don't like to work with relays. The solid state tremolo wiggler ...no fan of either
ah it's al very fresh, this idea. But the general sound of the tone king is very nice , that's why I came up with this idea...
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Heck.. I want to try building the imperial as is per schematic posted earlier. But I have zero knowledge about relays. Is that complicated?
The relays are not specified.. any idea which types I could use? Where can I find more photographic or drawn documentation on how I should wire these inside an amp for channel switching and trem activation? Help is welcome...thx
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Relay ? Some information to studies:
https://www.explainthatstuff.com/howrelayswork.html
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https://el34world.com/projects/relay_switch.htm
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I am going to draw a layout. Maybe you guys can help me out where I might/will get stuck...
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Help yourself with a Fender Deluxe Reverb Layout.
Forget vibrato circuit :
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_reverb_aa763_layout.pdf
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Help yourself with a Fender Deluxe Reverb Layout.
Forget vibrato circuit :
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_reverb_aa763_layout.pdf
Thx! Good tip!
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I started drawing a layout. Before I go on... anybody have remarks on this one? Is there certain trouble to be expected the way I'm doing it?
Still figuring out the relay part... I'm at the stadium in the layout where I have to implement them in the circuit.
As for the reverb... I want it always on on both channels. Guess I have to implement it later in the circuit? Between connections marked as 'X'? Looks like the area to put a passive FX loop too...
When I ditch the relays (don't need them for reverb) for channel switching and just use a DPDT, I can only switch channels by hand. Is there a way to use a footswitch instead? I'm thinking a standard fender double footswitch.. one for the trem and one for the channel. Heck I should do the relay thing, but don't know how...
The green+red turrets are where I have to proceed. It's The upper part of the preamp schematic I have put on the turretboard layout...
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There's basically 2 ways that I know of to do channel switching with a footswitch. Relays or opto-couplers. I've seen opto-couplers used is a couple of Fender amps, and Peavy tube amps. The relay method is more understandable to me now that I've built one. I got the parts from Hoffman's store and used the schematics listed previously, the ones on EL34 world. It works quite well.
The really old fashion way to do channel switching with a foot pedal is to build a footswitch box with 1 in and 2 outs. You plug the guitar into the footswitch box and switch between the outs. Those are plugged into the 2 channels of your amp.
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> ways that I know of to do channel switching with a footswitch.
BJTs, FETs, 2-ch opamp chips, JFET and CMOS switch chips, multiplexers. And Neil's wizzer.
And I suppose someone has foot-switched a lamp aimed at a motivated stage-tech to switch wires/knobs on demand.
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> ways that I know of to do channel switching with a footswitch.
BJTs, FETs, 2-ch opamp chips, JFET and CMOS switch chips, multiplexers. And Neil's wizzer.
And I suppose someone has foot-switched a lamp aimed at a motivated stage-tech to switch wires/knobs on demand.
Thát is extensive!!! Great throw at it 😄
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Anybody have some serious remarks on the layout I'm working on?
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Question: I would like to put in the bias vary trem of the Hoffman AB763 one-channel. Can I do a copy-paste of that on the Imperial? Should I change the plate resistor of the trem tube from 470k to 100k?
https://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf
Also, the reverb... That's a Blackface type reverb on the hoffman, no? It should outstand the ipmerial's reverb, which is kinda dull.. I mean, they bragg about the reverb being softer and more useable.. I think that's a bad thing, because the fender reverb is the best in it's league...
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Can I do a copy-paste of that on the Imperial?
the int pot will need a path to ground since your amp is self biased n Dougs is fixed
I would leave the 470k for the tweaking stage
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Can I do a copy-paste of that on the Imperial?
the int pot will need a path to ground since your amp is self biased n Dougs is fixed
I would leave the 470k for the tweaking stage
Can I conclude the 3rd lug to ground instead of to -50V , or both?
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Question: I would like to put in the bias vary trem of the Hoffman AB763 one-channel. Can I do a copy-paste of that on the Imperial? Should I change the plate resistor of the trem tube from 470k to 100k?
https://el34world.com/Hoffman/files/Hoffman_AB763_1.pdf
Also, the reverb... That's a Blackface type reverb on the hoffman, no?
Just copy the Hoffman tremolo EXACTLY. Keep the 470K plate resistor. However, the INTENSITY pot right lug (as seen on the layout and schematic) must be connected directly to ground.
Hoffmans AB763 reverb is blackface.
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question about the relay switching. I think I am starting to understand it, so I might keep things as is.. except for maybe the reverb....
To be sure I understand this correctly, could you look at the schematic attached here if it is ok?
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Not OK. The relay coils need to be connected in parallel, not series. I didn't even look at the contacts.
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ah..crap! I'll have to look at it again
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And suppose I put the relays in parallel? Do you think the connections are correct?
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Not even gonna guess. But if you'll draw the contacts in the schematic (not layout) I'll try. But ain't gonna flip between a relay drawing and schematic. Do your part.
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ok Steve...
I have adapted the relays on the schematic, like you asked...
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and here with the BF reverb mod
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You have too many contacts for K2 and K3. Hoffman's relays are all DPDT (equivalent to two SPDT in one box). There are two terminals for the coil. There are only six terminals left for the switch contacts.
K1 will work but a couple things... You call it a SPST but in fact it is a SPDT. And simplify your wiring. You only need one green and one red wire to the relay. Connect R18 and R20 directly together and run a single green wire to the relay. Likewise for C19 and C20.
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okay.. like this then?
by the way.. is there a very huge difference in using only 1/2 12AX7 for the reverb preamp instead of parallel? And if only 1 half is used, can the recovery share that tube half? That would be the one-tube reverb? I have that exact one-tube reverb in my Marble Clubreverb and it is VERY good. The only difference is that the marble has a 200k resistor in series with a .001uf cap from the middle lug of the pot to the PI grid..
Are these relays I can use? How many amps must they be able to handle?
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Nobody?
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That little Omron will handle all your relay needs on that schematic.
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That little Omron will handle all your relay needs on that schematic.
And the switching.. is that correct this time?
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Study this drawing. Label your contacts as COM1, NC1, NO1, COM2, NC2, NO2. Then we won't have to guess.
(https://el34world.com/projects/images/Img_7147.jpg)
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Study this drawing. Label your contacts as COM1, NC1, NO1, COM2, NC2, NO2. Then we won't have to guess.
(https://el34world.com/projects/images/Img_7147.jpg)
Thanks steve!! I was on the wrong track about how these switch. I assumed they switched like toggle switches. This is a very useful piece of information
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I understood your drawing but I was pretty sure that when you wired it up it would not work. You're on the good path now. Seriously though, label the contacts as I mentioned. Then everyone should understand your circuit.
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anybody have a schematic to power the switching relays via the heater wiring? The transformer on the schematic of the imperial has a separate tap for the relays, but the transformer I intend to use doesn't (hammond 290BEX)
It looks like I must be careful with the ground reference...
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https://el34world.com/projects/relay_switch.htm (https://el34world.com/projects/relay_switch.htm)
try this
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The imperial wires the center tap from the heaters to the cathode. I have the feeling that I can't juice the relays doing that. So my guess is that I don't connect the center tap to cathode. In fact don't connect the center tap at all and wire the relays according to the hoffman schematic?
Or maybe I can switch the rectifier tube to EZ81 or SS rectification, so I have the 5V tap left to juice the relays?
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Keep it simple. Just buy the smallest 6.3VAC transformer you can and use that for the relays.
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Keep it simple. Just buy the smallest 6.3VAC transformer you can and use that for the relays.
I drew out a schematic.. maybe that will work?
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Keep it simple. Just buy the smallest 6.3VAC transformer you can and use that for the relays.
something like this?
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is this circuit for the relays switching ok? I drew it with a separate power supply transformer 240VAC-6VAC
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Neither of those drawings will work.
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Where are the mistakes?
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Not trying to be mean but it's a very simple circuit. And the mistake is also simple. Stare at it until you say duh. I know you can find it.
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Not trying to be mean but it's a very simple circuit. And the mistake is also simple. Stare at it until you say duh. I know you can find it.
Ok I found some errors...
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Keep starin'... :wink:
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Keep starin'... :wink:
modified it again...
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maybe this DUH? connect the minus side to ground reference?
I'm just guessing right now... ah crap!!!
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Ok, I put the hofman schem aside and put the Imperial schem back on the table...
here goes:
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Duh huh. :thumbsup:
Now let me make a couple suggestions. Drop the two resistors. They're not needed. Remove the reference to H1 and H2 since this is a dedicated transformer used ***ONLY*** for the relays.
Seems you want K1 and K2 energized at the same time? So simply connect the two coils together (parallel). Don't loop the voltage through K1 contacts. While that will work, it's a bit klutzy.
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What is the coil voltage of your relays? If 5V, I suggest using a 7805 VR chip.
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thx!!
well..did you see the last post where I dropped the hoffman schematic and reintroduced the Imperial schematic? I seem to understand now what its says..
your post referred to the imperial schematic, or the hoffman?
I ordered a few things whil ordering the parts for my amp.
I found a 6V power supply kitthat should work for juicing the relays
I also ordered a 6V double relay switcher kit with stereo cliff jack and diodes,... included. I want to use that for 1 relay for the tremolo and the other for the channel switching. I also ordered a separate relay for the 2nd one on the channel switching. With those it's just a matter of figuring out the connections and I should be set.
For safety I ordered a few relays extra in case I have to follow my first plan. Also the diodes and 4700uf cap...
here are the links to the relay stuff I ordered
https://www.tube-town.net/ttstore/finder-relays-dpdt-125v-2a-6v.html
https://www.tube-town.net/ttstore/tt-kit-extra-power-supply-6-v.html
https://www.tube-town.net/ttstore/kit-double-relais-switcher-6-v.html
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your post referred to the imperial schematic, or the hoffman?
What I said applies equally to either schematic.
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I'm figuring out a layout for the amp. I've prepared the turretboard for the preamp and the filtercaps.
The reverb tx is to be built in that location underneath the chassis ofcourse. The location of the PTX, choke and OTX will be placed just like the DR. Is there anything in the layout that is going to give trouble for sure? What should I change?
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I thought of a new chassis layout. The blue cube is the relays power supply. I think of running the wires to the relays under the top corner of the backside and the heater wiring along the low corner of the backside. Maybe the rectifier tube should be in the front corner under the pilot light?
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The build is ready (amp chassis) and it sounds awesome!!!
https://www.dropbox.com/s/k7pm8migiki1fq4/Imperial%20build%20first%20recordings.m4a?dl=0
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99% finished. A few hardware stuff and the reverb bag ( have to beg my wife to get behind het sewing machine)
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Is there any hazard involved with the
Hoffman 1/4 power switch with resistors? I mean that on running the amp halfway.. not full throttle
Bump
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another thing I think is incorrect about the imperial schematic. It connects the screen grid to B3, which is only about 350V. It think it'd be better to downsize the resistor between B2 and B3 so I can raise that to 410V. Maybe I should try swapping R87 en R88's values so there is 5k between B2 and B3 / 10k between B3 and B4. That seems to make more sense to me.
Sad thing is I don't have any reference voltages for the imperial besides the 5E3 and BFDR voltages. the schematics of these are pretty similar to the imperial preamps. The PI is very different.
It would also make more sense to have a higher voltage on B3 for the reverb because the BF reverb has also got 410V on the plates of the send half and 170V on the platse of the recovery half.
anyway, the difference of +-80V between plate and screen on those 6V6's don't seem right...
and I think I will also try out what the effect of a bypass cap on the cathode from V1 will bring. There is none on the schematic, but maybe it's better with one? Both the 5E3 and the BFDR have one. OTOH it might be overkill for the OD channel, which shares that first preamp stage...
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Is there any hazard involved with the Hoffman 1/4 power switch with resistors?
What's the Hoffman 1/4 power switch? Can you provide a pic or a link?
another thing I think is incorrect about the imperial schematic. It connects the screen grid to B3, which is only about 350V.
I doubt that is a mistake. It's a good thing.
Maybe I should try swapping R87 en R88's values so there is 5k between B2 and B3 / 10k between B3 and B4.
That's how it is now. I'd let it be.
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Oops.. it has to be robrob
https://robrobinette.com/Generic_Tube_Amp_Mods.htm#Quarter_Power_Switch
Towards the B3.. I was just worried the voltage difference between the screen and the plates on the 6v6 was too large. The 5E3 and BFDR don't have that big difference.. don't want to ruin good new tubes
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+ I found it odd the schematic calls for a 250R cathode resistor.. but to get the bias at 85% range I had to put in 400R. With the 250R it was 113%
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That quarter power switch should work just fine.
+ I found it odd the schematic calls for a 250R cathode resistor.. but to get the bias at 85% range I had to put in 400R. With the 250R it was 113%
250Ω is the standard value used for P/P 6V6s. Cathode biased amps typically run at 100% or more. Not gonna hurt anything to increase the resistor value.
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Thanks
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Towards the B3.. I was just worried the voltage difference between the screen and the plates on the 6v6 was too large. The 5E3 and BFDR don't have that big difference.. don't want to ruin good new tubes
That voltage difference is not too large. Your new tubes will last much longer with the reduced screen voltage.
Fender and many other manufacturers run the screen at or near the plate voltage to squeeze out every bit of power they can. Doing so is hard on the tubes.
Heck, some of the big bottles, 6550, KT88, etc., run the plates at 600V and the screens at 300V.
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Well.. I tinkered around with some stuff and I think it's fatter and greasier sounding.
1. I put a B500k pot in series with R21, the last resistor of the drive channel right before the input of the PI circuit. By raising the resistance I can get the OD at a little less volume.
2. I put a 47uf 63V cathode bypass cap parallel with the 820R (R3) on V1. This beefs up the tone and makes it somewhat greasier.
Is there any harm in doing those mods?
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Bieworm, I realise this is an old post but just wanting to ask if you found the mid-bite channel anemic at first ... in your last post you said you put in some mods? I have just completed the build myself; I've put in a reverb similar to the Princeton and the bias wiggle circuit similar to the Ampeg J12B. Everything sounds great apart from the first channel - it hasn't got much bass and the mid bite isn't particularly effective. All voltages I have recorded are very similar to what you posted. If you get this then I can post my layout to see if there are any differences.
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Bieworm, I realise this is an old post but just wanting to ask if you found the mid-bite channel anemic at first ... in your last post you said you put in some mods? I have just completed the build myself; I've put in a reverb similar to the Princeton and the bias wiggle circuit similar to the Ampeg J12B. Everything sounds great apart from the first channel - it hasn't got much bass and the mid bite isn't particularly effective. All voltages I have recorded are very similar to what you posted. If you get this then I can post my layout to see if there are any differences.
While the standard TK imperial OD channel is fun, it would never be useable Iin a band setting. + the volume is close to uncontrollable if you want OD.
I did indeed do a lot of tweaking to that channel ending up with abrown medium OD marshall tone. Very nice! It also involved changing the paraphase PI into LTP PI... much more control over the volume overall.
Ignore that last post. I changed values since then...
Look at the schematic attached. Note that the 220k resistor circled in blue has landed on 100k. 220k took too much signal away, and no resistor at all made the clean channel interact too much with the OD channel.
Sound clip.. crappy phone recording
https://www.dropbox.com/s/4ztce46vyo1e8n7/Rockinbird%20full%20blast.m4a?dl=0
Please post some pics of your build. I wanna look at how you've done things..
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Thanks for coming back on this. I've attached a couple of pictures and the layout I put together - you'll notice that the preamp section is very similar to what you started with (I really appreciate you starting this post and sharing what you found). I opted for a standard Princeton style reverb and J12B style tremolo (Thanks to Sluckey for his redrawn J12B layout). Reverb and Tremolo are good.
I used Tubetown for the relays and they seem to work great. I did tap into the heater supply and don't seem to have had any issues with noise in the circuit.
I have also added power scaling (whole) amp to attempt to get overdrive at lower levels. I'm going to change this to the power section only and add a master... full amp just doesn't do it for the tweed channel.
The tweed channel just really doesn't do it. It doesn't seem to have much bass to start with and the mid-bite doesn't do it either. I will go through the schematic a few times and I'll put the scope on the amp.
I need to work out if I am losing the tone through the mid-bite section and whether I have made any mistakes.
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I meant to say that I'll have a look at your changes you posted (thanks :icon_biggrin:) and consider doing something similar. I wan't to work out what may be wrong. From what you said in your last post it takes a lot of volume to start getting the amp into OD territory.
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I meant to say that I'll have a look at your changes you posted (thanks :icon_biggrin:) and consider doing something similar. I wan't to work out what may be wrong. From what you said in your last post it takes a lot of volume to start getting the amp into OD territory.
The volume problem was countered with the change of the PI to LPT type.
The OD was too fizzy and at some point I just gave up on it. Too much frustration and excessive tweaking..altering...
I wired the OD to a setup I was sure I was going to like .
Funny to see my amp layout.. kinda😉😉😉
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The LTP would give you a bit more gain compared to the paraphrase… you may even get a bit of PI drive. Thanks for sharing your preamp section. I’ll try a couple of tweaks with the current circuit and may go down the same route as you. The Blackface channel and amp as a whole is brilliant. I am running on an Alessandro GA-SC64. BTW….first time I have been running on relays too.
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The LTP would give you a bit more gain compared to the paraphrase… you may even get a bit of PI drive. Thanks for sharing your preamp section. I’ll try a couple of tweaks with the current circuit and may go down the same route as you. The Blackface channel and amp as a whole is brilliant. I am running on an Alessandro GA-SC64. BTW….first time I have been running on relays too.
I changed the treble cap to 500p too on the BF channel. And I upped the mid resistor to 27k.. but I'm not a BF guy anyway😉
You're wrong about the LPT geving more gain than the paraphase. It's the other way around.. I tried to tame the gain/fizz. The LTP tamed that right away.
I also think design wise the last B+ filter cap has too many triodes on it. I will put this amp on the bench some day and add some more filter caps in parallel to sort that out.
I started drawing the schematic to completely separate the preamps and add another triode to go AB763 and 2204.. but I started other projects since then and put those ideas aside fir another time. Maybe that time has come... lol.
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Yep, your right on the gain of the paraphrase vs LTP … senior moment for me. Well spotted on the gain stages per node … ideally 2 per node. BF channel, I can see you like your mids with the 27k … I may give this a try. I’ll have a look at the current setup and work out what’s not right. I may go down 6G3 LTP but leave it cathode biased … it would be good to see if I can get a similar setup as the Imperial. It’s just not quite there
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Yep, your right on the gain of the paraphrase vs LTP … senior moment for me. Well spotted on the gain stages per node … ideally 2 per node. BF channel, I can see you like your mids with the 27k … I may give this a try. I’ll have a look at the current setup and work out what’s not right. I may go down 6G3 LTP but leave it cathode biased … it would be good to see if I can get a similar setup as the Imperial. It’s just not quite there
The 500p treble cap was a huuuuge difference too