Found an Old Mono Hoffman Record Player with 5E3 configuration

[Platefire]

I got to looking at this one this afternoon getting ready to start drilling some holes and had a change of heart. I'm going to make the Transformer side the front. Got to do a little re-figuring now. Plate

[Slimtim]

Yeah there's alot of dead space up under the trannies to put your preamp section.Still looking like it's going to be tight though.

[Platefire]

Well I dealt with tight before. Take a look at this Carman Gia circuit in this old Baldwin Chassis.
Plate

[Platefire]

An accident brought out some good news last night. I was working on this amp marking holes to be drilled and the amp accidently fell on the floor. Before I went any further I wanted to test the PT to make sure it was OK. So I did a temporary AC power hookup to PT with rectifier installed and it came up just fine but the surprise when I checked the DCV output of the rectifier was 360VDC unloaded. Originally It was at 259 DCV loaded with the old circuit, so I'm thinking with the new circuit it will be slightly over 300VDC loaded that would be more in line with the a vintage 5E3. ye haw!

Got a question??? The thought crossed my mind about putting a bottom plate on this chassis made out of Lexan or some clear material so the circuit is visable throught the bottom plate.
Has anybody done this before??? Platefire

[sluckey]

I have.

[Platefire]

sluckey--- details sluckey details!

1-did you use Lexan?

2-How did it work out?

3-Got any pixs? If you do, would you show your pixs?

[sluckey]

Details? What can I say?

I used 1/16" Plexiglas that I purchased from Lowes. Don't think it was Lexan. I just cut it to size using a utility knife to score a line and then putting a 1/2" dowel rod under the score line to snap. I touched up the edges with a sanding block and 80 grit garnet paper. Then I drilled 4 holes in the Plexi and finally attached to bottom of chassis using self tapping hex head sheet metal screws. Works well to keep the palmetto bugs out. Small critters can still crawl thru the 1/4" phone jacks.

I don't have a pic that actually shows the plexi installed but here's the chassis I put it on. See the 4 holes in the bottom lips? If you need to see what the plexi actually looks like when installed just tape a piece to your monitor screen. 



Wait a minute! Here's a pic that shows the plexi. Probably not what you wanted... 

[Willabe]

If you need to see what the plexi actually looks like when installed just tape a piece to your monitor screen. 

     

[Platefire]

Well that's about as close to a perfect lead dress as I ever seen. Makes my best lead dress look like a rat nest. Guess I'd want a piece of plexi over it to show it off too!

My experiance with plexiglass is that it gets scratched up easy. They were using Lexan as window glass at Fort Polk where I use to work and it seemed to be more scratch resistant but a little pricey.

I'm sure LOWES plexiglass would be fine for my low budget project and with the old 50's style point to point it will not be a pretty sight to behold. I was really wanting something thicker than 1/16" because I was planning on drilling some holes and installing some rubber feet. I'll look at Lowes and see what they got.

Since I don't have any plexiglass yet, i had to let my computer monitor screen substitute. It did give me a warm and fuzzy  
Platefire

[sluckey]

Just had to have a little fun with you Platefire. This retirement leaves me with way too much idle time.

[Platefire]

Ah Ha! Entertainment at my expense-----you know you could take up a hobby now to take up your extra time like amp building or something like that  


Been retired 3 years now after 44 years of working. I have no problem with quantity of things to do how, it's just doing them. In the absense of having a working boss to answer to anymore, my wife helps me with that now.   Platefire  

[Platefire]

Kind of thinking of giving this to my grandson as a practice amp. He's got a 100 watt Blackstar head with 4/12 cab as his main amp. So thinking of adding a MV for late night noodeling and also a DPDT switch for switching the V1 extra gain stage in and out for extra gain. Space is tight in the little chassis, so hopefully I can pull it off. He also has a Fender SS 2-12 amp plus a small fender practice amp--so with all that he should be able to fine a speaker to hook it up to. Platefire

[Slimtim]

nice gift and a good idea.How's it coming along?

[Platefire]

Got some parts ordered. I broke the Radio shack pilot light trying to tighten it up. Since I already had the hole drilled for the RS one, I bought another identical to replace it--haven't installed it yet, but will do so very carefully. I did a pencel sketch of my original circuit layout/hookup plan, so I'm having to re-arrange it a bit to make room for the MV, DPDT switch and extra parts. I'll need some extra terminal strips originally planned. Platefire

[Platefire]

On this 5E3 amp I was only planning to have one channel and use the other gain stage for extra gain. I was planning a DPDT to switch the extra gain in and out plus have a MV. I think it all should be placed between the PI tubr gain stage and PI stage. Can't say I've seen this done to a 5E3 before---is this workable of should I have the DPDT/MV right after the tone stack? Please check out my attached schematic and let me know what you think? Platefire 

[sluckey]

You need a 1MΩ resistor from V1-7 to ground. And you need a cap between the MV wiper and V2-7.

[DummyLoad]

that's a lot of gain. you may want to experiment with 2nd and/or 3rd gain stages not bypassed or at least switched in/out. also, with that much gain, sharing the same power rail the amp may be unstable.

--pete

[Platefire]

Thanks sluckey, revise sch attached.

Dummyload-Yep, a bit concerned about that because a 5E3 distorts pretty quickly without any help---so that's why I put the schematic up rather it is feasiable or not. Might be a bit over the top!

I was making it for my grandson which a bit of a metal guy that practices a lot. So I was thinking of the MV good for late night lower volume practicing and the extra gain stage for extra grind but it may be all too flabby to be useable.

I've been thinking maybe I should just do the one channel 5E3 first and get it tweaked and running right before I dump extras on it. The only trouble is real estate is tight and if those extras are going to fit, you have to include their space in the initial planning. Platefire

[Platefire]

Hump! doing a little research on the subject seems to indicate the MV I've drawn is not workable? I couldn't find a single instance that this type of mod had been done. Every conversation about that type of mod was negative. The only mod I found was where the PI design was changed and they used a seperate MV on each grid. Platefire

[Platefire]

Well I take it all back and wish I had said more  

I looked all over the net and ended up finding the best discussion right here at Hoffman:

http://www.el34world.com/Forum/index.php?topic=12365.0

I am assuming from what I read, this version of MV was the winner?
 

[printer2]

If you leave out the tone stack and ignore the NFB, Peavey has a master before the PI triode.

[Platefire]

The peavey has the same type PI but no gain stage after the tone stack like the 5E3. With the exception of the 220K grid restor, NFB Loop and the 100pf to ground the MV is set up just like my created schematic. So that gives me confidence maybe to try in my original way before I try it the so called bootstrapped way on the linked thread. Plate

[EL34]

Steve, That is some beautiful construction in post #56

[Platefire]

Doug, the discussion at #56 was about putting a piece of plexiglass or Lexan on the bottom of the amp head to make the circuit visable. Steve was showing the amp he had installed plexiglass on. With a circuit appearance like that you want a window so all can see. It seems in what we do a window to the circuit layout should be done more often instead of rare. Platefire

[EL34]

Yes, with beautiful construction like that, it deserves to be shown

[Platefire]

So for my Rat Nest old style p to p I probably need to use 1/4" steel and weld it up solid  

Har! I did pick up a $2 piece of plexiglass at LOWES this week. I didn't measure the chassis beforehand, the piece appeared large enough at the store but when I got home---to small!
I won't use 1/4" steel but will use one of the scrap pieces of sheet metal in the shed.   Platefire

[TIMBO]

Nice project Plate, These types of relics are very few around here and I too found it hard to walk by when I found a couple (one record player and radio record player)in a junk shop. I ended up paying $80 plus a roll of chain wire and a gate that was on the way to the tip  .
By the time I stripped out the dead stuff there wasn't much left but the leftover stuff is in the cupboard waiting for some "INSPIRATION" 

[Platefire]

Yeah, sometimes we beat our own self up for luv of toobs!    when I saw the tube chart on the back of the record player with 2-12AX7's, 2-6V6'a and 1-5Y3--the thought of a 5E3 dancing in my head wouldn't let me rest. I was kind of hoping it would be gone when I came back but it wasn't--so I had to do my duty!!! Last thing I need is another amp--so it's going to my grandson rather he wants it or not! I'm hoping he will appreciate it. Platefire 

[TIMBO]

I'm hear'n ya 

[Platefire]

I think I'll make room for the MV & hot switch but get it up and running as a one channel regular 5E3 first. Then when I get that working and sounding right, add the extras. If then they are doing more harm than good, I will know it. Platefire

[Platefire]

Got the new power supply wired up the other day and did a test. The existing OT is only delivering plate voltage to one power tube and on the other tube-nothing! So I have a DRRI OT and wondering if that would work? even though the voltage level will be 5E3 levels and not AB763? The DRRI OT is about twice a big as the existing but I think I can squeez it in if it would work properly. Platefire

[sluckey]

That'll work.

[Platefire]

Muchas Grachias Amego!

[Platefire]

Installed the DRRI output transformer yesterday and finished wiring up the amp. It sounds good and strong. A lot cleaner loud volume than I expected. The preamp and PI voltages are running kind of high even though I used the perscribed power gird and plate resistors---not sure what's going on there. Now that I know the amp is worthy and what normal operation sounds like, guess I can prceed with the mods for MV and a hot switch to kick in the other V1 gain stage. The tone stack is set up for the bright channel and no normal channel. Platefire

BTW-I used the old Hoffman 6V6's and 12ax7's along with the original RCA 5Y3 and they are all working very good.

[Platefire]

Here is the schematic with voltages for the Record Player amp. I think the reason the preamp voltages are high is because I haven't hooked the un-used 12AX7 gain stage to the power supply yet--so part of the normal load is missing. Platefire

[Slimtim]

sweet,let's hear it.

[Platefire]

I bought a piece of plexiglass from Lowes for this amp. I didn't measure the amp, just said "this looks like it would fit" in the store----got home----too little

Thanks for the Plexiglass/Lexan lesson---have no idea what your talking about  

But that plexiglass scratches so easy and is kind of dim. Don't guess there is anything really durable and clear too?

Regarding a sound clip. My computer has crashed with viruses two times this year in spite of having virus protection bought and paid for! So a lot of my tools have got blown out of the water. About the time I start getting my computer stuff together it goes south again  


BTW-I think this little throwed together 5E3 conversion sounds better than the brand new 5E3 I just finished. The only thing really different is that old 50's PT and that DRRI OT that I used. 

Platefire

[woolly]

the good sound is probably those old tubes. 

[Platefire]

That very well may be it. The amp just sounds more juicier if you know what I mean. The PT voltage output turns out to be perfect for vintage 5E3 levels. Platefire

[Platefire]

Now I know one of the reasons why this amp is sounding juicier than the other new one I just completed. It has the old Hoffman 12AX7 in V1 while the new one has a EH 12AY7 in V1.
I didn't have an extra 12AY7, so I tried a JAN 5157. Sounded good but I like the Hoffman 12AX7 better in V1, so it's back in there.

Also discovered I had the 500pf cap hooked up wrong on the tone stack and the tone stack was not effecting the tone no matter how you turned it. So got that corrected.

Well I'm trying to play at a lower volume these days. I thinking of trying a 12AX7 in V1 now on the new one. This is sounding and feeling pretty fine to me. Platefire

[Platefire]

Well the amp is tested and working fine. Trying to decide rather to go with the original plan for a hot switch and MV or rather to just make it a stock 5E3. With the 5E3's early breakup, I'm not sure how well the Hot switch and MV would work? From my reading other post regarding 5E3 MV, it seems nobody was too happy with the results?? I haven't read anywhere where someone has installed a hot switch in a 5E3, so am I treading on new ground there?

I guess where the rubber meets the road is just try it and see. 

[Platefire]

You need a 1MΩ resistor from V1-7 to ground. And you need a cap between the MV wiper and V2-7.

Sluckey, I have a previous build/conversion of a Revere reel to reel where I did a similar mod.
The schematic is attached. It worked pretty good but did have a squeal when I turned it to almost full volume--I think it may be because I don't have the 1 meg to ground in the same location you told me to add above in the quote. Also I don't have a cap between DPDT switch and PI on this one either. I'm not totally sure but I think I don't need a cap on this one because it's not directly connected to the cathode on this one. The schematic of the old build is attched, please take a look---I might need to make some corrections on this old build based on your advise on this build!!! Platefire

[sluckey]

The two amps are different in such a way that that advise doesn't apply to the old Revere conversion.

You don't need the 1MΩ in this case because when the switch is up you have the 1M volume pot connected to the grid and when the switch is down the grid is connected directly to ground.

You also don't need the cap feeding into that type of PI since the grid should be at zero volts for proper bias.

[Platefire]

OK, I see what you mean. Thanks for checking it out for me. Platefire

[Platefire]

This 5E3 is up and running very well with one bright channel. Getting ready to use V1b as hot switch gain stage and add 1 meg MV. I was thinking higher gain usually darkens things up. Would it be a good idea to go a little brighter on the coupling cap for this stage? on hand I got a .01, .033, .047. Haven't got any .022 on hand. Schematic attached. Plate  


EDIT: The .01 is just a hair smaller/brighter than the .022 on my schematic, so I think I'll go with that. 

[Platefire]

Ok It's kind of like Dummyload said in Reply #66--too much gain.      I finished hooking up the additional gain stage, MV and DPDT hot switch as on the attached schematic. The good part is with the hot switch off the MV works great with just the clean normal 5E3 setup--I like it! But---but when I turn on the hot switch it is way over the top as follows:

1-The tone and harmonics of the distortion is good with the hot switch engaged it's the gain that is out of control.

2-You can set it in clean with a good pre gain setting, MV and tone setting and flip the hot switch and it will just squeal the gain is so much. Then you turn the volumes way down to get it under control and if the switch back to clean mode the volumes is then to low for your previous clean setting.

3-With the hot switch on and extreme gain settings on the volumes, I got some motorboating.

4-Also with all the extra gain engaged, I get a little screach noise when I turn the tweed tone stack up to about 75% or more.

I could use some advice on how to get this under control so when you switch from one mode to another it want be such a vast difference. First thought that came to mind was install another volume control for the other gain stage??? Suggestions please. Platefire

BTW-When I lit up the extra gain stage for the hot switch voltages on V1 and V2 came down significantly--more than I thought they would. The new voltages are reflected on the new schematic.  

[sluckey]

I could use some advice on how to get this under control so when you switch from one mode to another it want be such a vast difference. First thought that came to mind was install another volume control for the other gain stage???

Start by removing the cathode bypass cap on the hot stage. Then increase that 10K between the switch and the grid of the hot stage to about 470K. If that still has too much gain then replace the 1M grid resistor on the hot stage with a 500K or 1M volume control.

[Platefire]

Thanks sluckey

I was originally thinking that a volume control on the output of the hot-switch gain stage between the .022 cap and DPDT switch would be the ultimate control but I guess when you you switch the hot switch on, all the amp gain stages in the grid become one continuous loop to the PI and that wouldn't work like I hoped, right?

So what your recommending is gain blocking/cut measures. Is the 1 meg vol you are referring to replacing the 1 meg resistor to ground with a 500K resistor or 1 meg vol pot? I haven't done the hot switch except only one other time and that amp was rather low gain--so I didn't have these issues.

I would really be interested in having a separate volume control for this hot switch but with this current setup it my not be possible. If there is any easy way to accomplish it, I would like to hear about it. Platefire  

[Platefire]

Pretty much concluded with all the gain stages switched on in series with the hot switch, no way to isolate the hot switch operation with a separate volume without effecting everything downstream.

The good news is the distortion/hot switch sounds pretty awesome IMHO. The best sound is with the MV 100% and just use the pre-gain vol--I guess because the power tubes are contributing to the the distortion too---you talk about Marshall like bottom crunch--pretty tough sound. The more you turn back the MV and turn up the pre gain vol you loose the heavy bottom but even with that the sound is pretty impressive. It just when you get in the extreme settings(MV at 9:00 oclock/Pre gain at 3:00oclock) is when the motor boating starts. Also the tone stack starts too squalk past 2:00 oclock when at the extreme settings.  

So the end result is with the hot switch off the clean setting works great. The MV works just like I like a MV to work. The hot switch on setting works great too as long as you stay away from the extreme settings. Platefire  

[Platefire]

My Grandson I'm building this for name is Devin, so I decided to call it the "Devinator". He graduated high school last year and is now going to collage. I did do a search regarding that name and it turned up a Rap group in Canada--so don't think no conflict there.  

This last weekend I built the bottom cover plate, painted it today and installed the bottom plate complete with rubber feet. Fired it up and ran it through the paces after I got it all back together and ready to go. I'm really happy with the way this turned out and as usual, thank you all for the help. Soon as I get some finished pictures done, I will post them. Platefire