I'm planning on building a stereo amp soon. I have some nice UL output transformers that came from canadian made amps - Electrohome pa-600 monoblocks. I also have a hammond 272jx PT (300-0-300 287ma , 8amp 6.3v and 4amp 5v)
I'm looking to use SS rectification and try not to use chokes. The unused 5volt winding might be used to give a little boost to B+.
Anyway just thought I'd ask you guys if you had any recommendations or favorite circuits that would meet my goals of no additional iron..
The Outputs historically had kt-66 power tubes connected.
I was looking at maybe trying the altec 345a with no dual 5u4s and ultra-linear connection.
Thanks in advance for any replies.
I'm looking to use SS rectification and try not to use chokes. The unused 5volt winding might be used to give a little boost to B+.
Anyway just thought I'd ask you guys if you had any recommendations or favorite circuits that would meet my goals of no additional iron..
The Outputs historically had kt-66 power tubes connected.
I was looking at maybe trying the altec 345a with no dual 5u4s and ultra-linear connection.
Thanks in advance for any replies.
Attachments
Nice project.
To get max. B+ boost add the 5 volt winding in series with the primary.
Regards, Gerrit
To get max. B+ boost add the 5 volt winding in series with the primary.
Regards, Gerrit
Given you have the Electrohome transformers (assuming you mean output trannies) why not just build the pa600? It's a Williamson, and should work fine.
This won't really address your question, but genuine Williamson output transformers are very rare these days and a "true" Williamson is a beautiful sounding amplifier. You'll need a better power tranny, in fact a pair would be much better for monoblocks. The Hammond 278X would be ideal, along with the 193D choke. You could replace the second choke (T1) with a 150 ohm/2 watt resistor without penalty (that's what I do in my Williamson builds) and substitute a single 22K/2W resistor for R9 and R13 to simplify matters a bit.
But this is not in line with your goal. I hate to see good Williamson outputs repurposed, but they certainly can be.
But this is not in line with your goal. I hate to see good Williamson outputs repurposed, but they certainly can be.
Thanks for the responses./advice. a pair of monoblocks would be nice. I would like to keep the cost down but I guess I could "save up". I have the 272jx sitting there unused and would prefer not buying more transformers right away. I do appreciate your advice on the power, choke and resistor plan,
Last edited:
Here's an offbeat Japanese design that I'm going to try this winter. I'll use a 272JX and with SS rectification and should have about 350 volts B+. The JX has lots of filament current for KT66s. The output tubes in the Japanese circuit are more or less a 12-volt loctal base 6L6GA or GB, so KT66s aren't too big of a leap. I'll be using 7581 or 6P3S-E outputs. Don't be choke-averse. They don't cost a lot and can help.
S.
S.
Attachments
Understood. ;-) Here's a budget stereo idea--an Antek AS-3T350 with SS diodes will get you about 430-440VDC at the output tubes, good enough for the Electrohome design. Use a pair of Hammond 159Q's (7H/150mA), one for each channel to split the supply. I've tried the Antek on my "hacker" Williamson chassis's I use for testing various OPTs. Worked very nicely.
@ Steve, that looks like a cool amp!
@ Grover, I actually do have 2 - AS-2t350's unfortunately one is being used in another build, it's a 2a3 stereo amp. Thanks for your advice once again! Good ideas!
@ Grover, I actually do have 2 - AS-2t350's unfortunately one is being used in another build, it's a 2a3 stereo amp. Thanks for your advice once again! Good ideas!
I think the spare Antek would serve for a stereo Williamson amp. Use one 6.3V tap for each channel with a hum-balance pot as shown in the schematic. I would definitely use chokes in the PS, it will render the amp quieter and more stable. That would be your only added expense. Other than that and some film caps for a split power supply, you're pretty much there. A good Williamson amp offers a wonderfully natural sound.
Last edited:
Okay that sounds good! I also just remembered I have an acquaintance who mentioned some time back that he had several power transformers that he would like to sell. I just looked up the list and there was a 278x and the closest one to that was a 274bx. I may be able to get those a lot cheaper than new if he still has them. I would imagine the power difference would be inconsequential. However the Antek looks like a the most probable. I have always wanted to try a Willamson build. I have never heard one before.
Here are mine, two of them built in 1960, PP 6L6GC UL.
6AU6 front end into a paralleled both sections of a 12AU7 driver.
Each have their own Hammond 273BZ PT & GZ34 Rectifier.
Used for 17 yrs till I bought a Sansui AU717 & matching tuner.
Attachments
@jhstewart9 , I assume you meant 273bx, no? I just read a little about au717 from back in 78! Still a sought after piece!
The monoblock amp in the pic looks nice and 70's calc is a nice touch!
The monoblock amp in the pic looks nice and 70's calc is a nice touch!
The 274BX works great with a 5AR4 rectifier. The 278X will work well with a 5V4. The Williamson is flexible--anywhere from 400 to 450 VDC B+. Up to you. ;-) I prefer a tube rectifier but the Antek with SS diodes gives you a bit more "grunt," of course, without the sag in the PS. The nice thing about the Electrohome circuit is that they have the feedback and compensation dialed in for those outputs.
Thanks grover, and the feedback point is a good one. I appreciate your help!
I see on the list of for sale items there are a pair of w-5m chokes too. Looked at the schematic and it says 7h 150ma 160ohms. So not exactly the chokes called for but close enough. Going to call this guy tomorrow and see what's left!
About the power transformer, I use a 372jx (110...240v version of 272jx) in a 28W stereo amp, solid state rectifier, no choke, gives 405v as idle (190mA total).
Take a look at the KT66 Mac Gyver amp. The schematic shows a choke load on the input tube, which I later changed to a solid-state CCS that actually works better than the choke.
Back in those daze Hammond offered two kinds of mountings for some of their transformers.
But in the long haul not enough of the 'Z' mounting were sold & they where discontinued.
The HV filter is 40 microF, 1.5H, 35 microF. The choke is a Hammond 153 buried inside the chassis.
The PS ripple is 0.4 v p-p. The OPT is something brought in from Japan labelled REX. It came with a freq plot.
There are both AC & DC balance pots as well as a bias pot in the circuit.
The front end is a 2-stage HP filter to block LF transients that would cause serious intermods
to the rest of the program material should the amplifier or loudspeaker be overloaded. Something most ignore.
The 2-tone IMD test was done using a PicoTech 3224. 👍
Attachments
@jcalvarez , Yeah i thought I might be able to squeeze a little bit more voltage if I connected the 5v tap too!
I'm going to be using same very efficient speakers too. I am still considering the 272jx.
@mbrennwa, cool circuit! I think grover makes a good point about staying with the pa-600 circuit for the reasons/points he makes above.
I did manage to contact my man with the iron for sale and he has all of it still. If i take the 2 power and 2 chokes he gave me a very reasonable price.
The only thing is the slight difference in power one being 375-0-375 and the other 400-0-400..
I think I'm going to spend the extra shekels and build the monoblocks. The wife being the good woman she is, gave me her blessing 🙂
@jhstewart9 Nice amps, are they sitting unused?
I'm going to be using same very efficient speakers too. I am still considering the 272jx.
@mbrennwa, cool circuit! I think grover makes a good point about staying with the pa-600 circuit for the reasons/points he makes above.
I did manage to contact my man with the iron for sale and he has all of it still. If i take the 2 power and 2 chokes he gave me a very reasonable price.
The only thing is the slight difference in power one being 375-0-375 and the other 400-0-400..
I think I'm going to spend the extra shekels and build the monoblocks. The wife being the good woman she is, gave me her blessing 🙂
@jhstewart9 Nice amps, are they sitting unused?
Those would work just fine. I've used them in several Williamson builds. All the Heathkits W1 through W5 were Williamson designs.