Altec 1567 Mods

[tablebeast]

I have wanted one of these to mod for a while, but was never willing to pay what they cost. I recently got one in trade filled with 4x 4722 input transformers and a 15095 output transformer. It is nice, clean, and totally stock. I want to do some simple mods while I restore it. All electrolytic capacitors will be replaced of course. It is actually a 1567A and I like it stock, but I think I can get more headroom and control over it with some tweaks. The mods I have planned include:

1. Install 1/4" switched jacks for Hi-Z DI Input on channels 1-4.
2. Replace ceramic caps in the EQ circuit with poly and silver mica caps.
3. Tweak the values in channels 2, 3, and 4 of the mixer.
  a. Channel 1 stays stock, Channel 2 swap the 220K plate resistor for 100K and 50uf bypass cap for 470uf. Add .1uf grid cap to each.
  b. Channel 3 change cathode resistor to 1K5 and bypass cap to 25uf. Change .1uf plate cap with .022uf. Add 68K grid resistor.
  c. Channel 4 change cathode resistor to 820R and bypass cap to 250uf. Change .1uf plate cap with .047uf. Add 22K grid resistor.
4. Change EQ 12AX7, both sections from grid leak type with grounded cathode to 1K cathode resistor, un-bypassed.
5. Swap channel 5 line level 250K-A control for pre-master volume at end of EQ circuit, move master volume control to front of 6CG7 circuit
6. EQ bypass switch.
7. Add 1K grid stopper resistors to 6CG7 dual inputs.
8. As for replacing the electrolytics, I will go bigger as space permits.

As you can see I don't want to do anything drastic. No need to rethink the wheel. Changing the channel 5 line input pot with the 500K-A master volume pot allows me to move the 500K-A master volume to in front of the 6CG7 section and now I have three gain stage controls for fine tuning gain and distortion while keeping it from clipping! I will get a redrawn schematic up soon. If anyone has a GOOD .jpg scan of the original it would be a big help as the one floaiting around the net in PDF form sucks with some values impossible to read. So, comments, questions, suggestions?

 

[lassoharp]

I have wanted one of these to mod for a while, but was never willing to pay what they cost. I recently got one in trade filled with 4x 4722 input transformers and a 15095 output transformer. It is nice, clean, and totally stock. I want to do some simple mods while I restore it. All electrolytic capacitors will be replaced of course. It is actually a 1567A and I like it stock, but I think I can get more headroom and control over it with some tweaks. The mods I have planned include:

1. Install 1/4" switched jacks for Hi-Z DI Input on channels 1-4.
2. Replace ceramic caps in the EQ circuit with poly and silver mica caps.
3. Tweak the values in channels 2, 3, and 4 of the mixer.
   a. Channel 1 stays stock, Channel 2 swap the 220K plate resistor for 100K and 50uf bypass cap for 470uf. Add .1uf grid cap to each.
   b. Channel 3 change cathode resistor to 1K5 and bypass cap to 25uf. Change .1uf plate cap with .022uf. Add 68K grid resistor.
   c. Channel 4 change cathode resistor to 820R and bypass cap to 250uf. Change .1uf plate cap with .047uf. Add 22K grid resistor.
4. Change EQ 12AX7, both sections from grid leak type with grounded cathode to 1K cathode resistor, un-bypassed.
5. Swap channel 5 line level 250K-A control for pre-master volume at end of EQ circuit, move master volume control to front of 6CG7 circuit
6. EQ bypass switch.
7. Add 1K grid stopper resistors to 6CG7 dual inputs.
8. As for replacing the electrolytics, I will go bigger as space permits.

As you can see I don't want to do anything drastic. No need to rethink the wheel. Changing the channel 5 line input pot with the 500K-A master volume pot allows me to move the 500K-A master volume to in front of the 6CG7 section and now I have three gain stage controls for fine tuning gain and distortion while keeping it from clipping! I will get a redrawn schematic up soon. If anyone has a GOOD .jpg scan of the original it would be a big help as the one floaiting around the net in PDF form sucks with some values impossible to read. So, comments, questions, suggestions?

Seems that a lot of people get these for their distortion characteristics - esp on elec guitar so I'm kind of surprised at the effort to move away from stock performance in that regard.  The 1st stage is usually the most susceptible to clipping and the cleanest way to deal with that is an external pad or variable attenuator for finer control.

Given the outrageous market prices for these I personally would shy away from drilling any holes simply because of the possibility of losing resale value.

I use mic mixers/amps all the time for line level apps and deal with it by making mic cables with built in line to mic pads.


As for the grid stoppers I'm not seeing where you're headed there unless the different value plate/cathode resistors you mentioned adding cause the circuit to become unstable.  If that's the case I guess it's a matter of weighing the advantages the proposed tweaks are intended to give vs the possibility of the amp oscillating.  I've played with coupling cap values on a Langevin PP circuit and it squealed when within 1 1/2 standard values off . 

What do you wish to accomplish with the individual channel tweaks?

 

[mrclunk]

We have one of these, i like the sound 'as is'. But would be interested to hear about any mods you do.
The only changes i made to ours was to select a couple of input valves with very different characteristics. One Mullard thats fairly clean/smooth and a gnarly Sovtec for more bite and crunch.
There was an interview in TapeOp #73 on Jay Bennett which reminded me to have a poke around inside ours.
Jay Bennett about the 1567a :-
"A lot of people think they're to noisy, Thats because they don't know how to fix them. I do and i'm not going to tell anyone else."

 

[tablebeast]

Jay Bennett about the 1567a :-
"A lot of people think they're to noisy, Thats because they don't know how to fix them. I do and i'm not going to tell anyone else."

Way to go Jay, now you're a dead dick and your magic knowledge will be forever hidden. Ha, what a selfish prick. I share whatever I've got, no info is sacred. I'm sure I'll be able to 'fix' this guy better than Mr kicked-out-of-Wilco could ever do.

By the way, my mods don't aim to change the distortion profile, just get more control over it for distortion sculpting. I've always hated the sound of ceramic caps in the audio patch and the way grid leak type circuits distort, by changing these things, adding a gain control at the grids of the 6CG7 and giving a varied collection of inputs I think I can do a lot to make it sound more like I wait to. I decided not to drill any holes, just rearrange what is there with the tag strips.

 

[emrr]

Way to go Jay, now you're a dead dick and your magic knowledge will be forever hidden. Ha, what a selfish prick. I share whatever I've got, no info is sacred. I'm sure I'll be able to 'fix' this guy better than Mr kicked-out-of-Wilco could ever do.

classy

 

[tablebeast]

Way to go Jay, now you're a dead dick and your magic knowledge will be forever hidden. Ha, what a selfish prick. I share whatever I've got, no info is sacred. I'm sure I'll be able to 'fix' this guy better than Mr kicked-out-of-Wilco could ever do.

classy

EMRR, I was hoping if you replied it would be with some of your mods, anything to share there? I will be digging into this guy this upcoming week and was just trying to collect info before I did so. If no one has anything to add then I will just do this by myself like I have with all my projects for the past few years. It had been a while since I had been on this forum and had hoped I could get a real conversation going about mods that improve the 1567 as it looks ripe for tweaking.

 

[emrr]

I kinda hate these units; my suggestion with these is always to sell for a lot and build or buy something more useful and sensible.  The cost/resale value/usefulness ratio is all wrong with these. 

 

[Tubemooley]

So you had hoped to get a real conversation going by calling him a dead dick and a selfish prick? That worked out really well, didn't it? Keep that going for us, will ya..... Wouldn't it be safe to assume that no one has anything to add and you should just do it by yourself like you have with all your projects? Do you even need us? It sounds like you don't. Ya know..... It has been a lot quieter and peaceful here on PP without the beast for the past year. Maybe you're the dead dick. Did you ever think of that? By the way..... I want to do a Three Stooges version of my Speak-n-Spell. Can you help me with that Mr. Beast? Or am I a dead dick too? Please Mr. Science.... please help all us losers out here. DW.

 

[tablebeast]

So you had hoped to get a real conversation going by calling him a dead dick and a selfish prick? That worked out really well, didn't it? Keep that going for us, will ya..... Wouldn't it be safe to assume that no one has anything to add and you should just do it by yourself like you have with all your projects? Do you even need us? It sounds like you don't. Ya know..... It has been a lot quieter and peaceful here on PP without the beast for the past year. Maybe you're the dead dick. Did you ever think of that? By the way..... I want to do a Three Stooges version of my Speak-n-Spell. Can you help me with that Mr. Beast? Or am I a dead dick too? Please Mr. Science.... please help all us losers out here. DW.

You are such a child. No one on here knows who I am. You show your cards by getting too personal. SOOOOOOOOO OT. Thanks for reminding me why I stay away. All I was doing was trying to lay out a comprehensive restomod for this device which is very common and looks like it can so easily be made more interesting. Since there were no GOOD posts in the archive I thought I would try to have one. Now you have ruined that, Tubemooley, with your childish rant. Go suck your thumb.

 

[Johan]

I know some people think the 4722 are over rated, but I have two and must say there is something special happening when you let a SM57 slam the grid of a 12au7 through one of them...just an opinion thou.. 
j

 

[tablebeast]

I know some people think the 4722 are over rated, but I have two and must say there is something special happening when you let a SM57 slam the grid of a 12au7 through one of them...just an opinion thou.. 
j

I love the 4722. Even better than as a mic pre, they make a AMAZING step up converters for MC vinyl setups. I am going to build a pair I have for just that purpose soon.

 

[lassoharp]

One other thing from your original list of proposals-

"Swap channel 5 line level 250K-A control for pre-master volume at end of EQ circuit, move master volume control to front of 6CG7 circuit"

This has been covered in other posts as general guidelines for interstage vol controls, but if I'm reading you right you'll be putting the 250K in place of R31 - the 1 Meg grid resistor on the 6CG7. This puts it within a NFB loop between V3 and V4. This may very well work against the fine gain tuning. Disconnect the loop first and see what happens. It could be drastic.  Also 250K will drop the loading on the V3b plate quite a bit - looks like in half. 

 

[tablebeast]

Thanks for thwarting the hijack guys. I will hold off on the master volume tweaking for now, but I have got to do something about that EQ stage, mine gets kind of fizzy and I think if I get rid of the ceramic caps and the grid leak bias, plus install a bypass, that it will really open this guy up. Does anyone have a schematic that is NOT from the commonly distributed online pdf? I would love to get a high res scan of the schematic if it is out there.

 

[Tubemooley]

B-A bay, B-E bee, bee eye bicky bye, B-O bo, bicky, bye bo bee you boo bicky by bo boo..... Come on.... Three Stooges speak 'n spell. What can't you decode from the schematic? Can't you read the schematic? If the schematic shows all the components and their values, then what is missing? I am just trying to remind you why you stay away. Where's my money? Send me my money. I don't usually suck my thumb. But I suck other things. For 300 an hour, I'll suck almost anything.

 

[emrr]

tablebeast, why don't you walk away from this one, and re-start the topic?

 

[b2]

Hi,

I'm working on the schemo of this 1567a, i've printed this circuit and I've some pb with the value of caps c8,it's seems to be .80mmf??But I'm not sure...If someone could give me the value of this caps

Thank's!!

Best regards,Bruno.

 

[lassoharp]

Hi,

I'm working on the schemo of this 1567a, i've printed this circuit and I've some pb with the value of caps c8,it's seems to be .80mmf??But I'm not sure...If someone could give me the value of this caps

Thank's!!

Best regards,Bruno.

.8mmf is what it looks like to me.  That's a tiny value cap.  I could only find disc ceramics at Newark that go that low. Micas start at 1pF. Films at 3.5pF.  Tantalums not even close.  Not to be worrisome, just to weigh the odds of the "8" being a 3 or a 5 based on commonality.

This needs to be here for a productive post.  It ain't the best but it ain't the worst.

http://www.triodeel.com/al1567a.gif   

 

[Mark Burnley]

Hi,

There's a clearer schem here-

alteclansingunofficial

I've restored a few of these now- great if you want that sound!

...hot output too.

Mark

 

[rickc]

c8 is 150pf. might be 180pf. both are standard values, but my money is on 150pf.

I could go look inside real unit.

 

[craigmorris74]

These get slammed all the time as being nothing but character boxes, but they were installed in many great American studios in the 50's and 60's.  The Clovis, NM studio where Buddy Holly recorded had these-never seen any other mixers/pres in pictures-and his records sound great IMO.
Craig