My VTA ST-120 is on the way .....and other loose ramblings of an old fart

My VTA ST-120 is on her way.
Last November I scored myself a sweet 1974 Fender Twin-Reverb guitar amp (arguably the "holy-grail" of guitar amps) and got hooked on tubes once again.
A couple years ago I built me a hybrid (switchable) Solid-State / Thermionic preamp with tone-stack which is my go-to preamp in my home studio (avatar pic).

So since I've gone tube-crazy again, I figure I will be no doubt rolling tubes soon, to this end, last weekend I built myself a tube tester that's capable of indirectly (some simple arithmetic involved) measuring transconductance, so I hope to roll some tubes.  When I was a kid, my uncle and aunt were the dealers for "Murphy Radio" here in Trinidad, when they retired and closed the store, I was given quite a stash of tubes (wish I could find those now!)

Present power amps in the studio are Alesis RA-500, and a couple genuine el-cheapo Class-D offerings from Amazon (Monoprice 300W $115 and a really tiny Nobsound 100W $45)  ......I actually love those two el-cheapo amps and the Nobsound is presently offering some Elvis through my speakers   ....they actually, surprisingly, sound awesome.

My main speaker system is Altec Voice of the Theater A7 with home-brew passive crossovers. Recording and mixing monitors are powered Edifier R1280T

Hoping to post some pics, but not sure if this forum will let me do so today (pretty new to this forum). Nonetheless, I will be documenting my ST-120 build here.  

Really like dealing with Bob and now looking forward to receiving the amp and contributing here when and where I can. Have a full electronics lab and a pretty darned decent machine-shop out back.

Ok I'll ramble on a Sunday afternoon. A-7, a 511 or 811 horn on the top, 808a driver, 4218-h 15" speaker in that huge enclosure. I carried several around on the band circuit in the early 70s, and changed many a driver as the cab handled all of 50 watts I believe and crossed at 500k. Enough for one Mark III. I built several MKIII kits to pair with four A7s and it was a very decent setup for its time in the early years of r&r. But then things went colosseum and the Mark III/A7 became underpowered. I still have all components laying around, less the cab of course...there is a limit! This is also why all my Dynas have 1/4 inch input jacks plus added quarter inch speaker outs on the chassis, which is heresy among stereo buffs and Dyna lovers here. Ruins the value. But they were a punchy, excellent amp well priced especially the kits, dependable and rough. I loved them and still have two, plus a ST70. Only issue was the tabs on the trannys tore lose hauling them on the road.

Yeah, back then when I was doing the local truck-borne Carnival music circuit (live band and DJ) I recall using ST-400's and Phase Linear ....don't recall what the speakers were though. Then my brother and I became the local Peavey dealers so it moved to CS-800's, CS-400's, Bass bins and Project One systems ....all fueled by copious amounts of rum!
Those were the days!

https://2img.net/i/fa/pbucket.gif ....guess,I still can't do pics

If you used the Phase Linear on the road then you certainly became an expert at replacing transistors in the field, they chewed through them pretty quickly. Also have one of those sitting in the basement taking up space. The CS800 was a tank. Seriously. Dropped one 7 ft. out of a trailer on concrete. Worked.

Certainly brings back fond memories!   ....CS-800's were certainly workhorses!   ...I spent a week with Hartley Peavey and his engineers in the 80's at the plant in Meridian and there were numerous roadie tales of dropping CS-800 at gigs and just dusting them off!  
...yup, those PL's eat outputs for breakfast, I believe we had a 12,000BTU A/C unit blowing right on them in the rack, the last time we used them

Just figured out how to post Some pics:

Recent build, my Tube Tester panel:
http://www.valveheaven.com/2015/03/an-inexpensive-easy-to-build-diy-valvetube-tester/


Electronics section of my workshop (the man-cave):


My preamp (BTW, I've long tossed that EQ unit). The Preamp's panel was done on this bad-boy which I built a few years ago:
https://youtu.be/X8q04zsvzT4


....and here's my 4-axis CNC Milling machine at work:
https://youtu.be/vSidwA-XA6g

Feel free to browse my crazy Photobucket Stuff:
https://s112.photobucket.com/user/cberkeley/library/?sort=3&page=1

This morning I lost the long speaker wires and went with short (10') cables from my Class-D amp to the VOTT's. The sonic difference was quite impressive, listening to Andrea Bocelli.  So the ST-120 will sit right between the VOTT's and as such I just purchased a befitting cabinet for the ST-120, CD Transport, CD's and some of my other stereo stuff and guitar accessories.
https://www.amazon.com/Michael-Anthony-Furniture-Highboy-Console/dp/B00ZOJJP2Q/ref=sr_1_3?ie=UTF8&qid=1519489984&sr=8-3&keywords=merako

Holy cow Cletus!... You don't mess around when it comes gear and test equipment. As a long ST-120 owner you will find it sounds great and extremely good value.

Nice toys on the bench!

Have fun, and follow the step by step (inch by inch) instructions included with the kit. I checked off each line item as I went along, highlighting the "solder later" steps. Once "done" I went through it all again, checking off the steps again to verify nothing was missed and bonus, getting another up close look for cold solder, bridges, and such. Check all your test voltages, and do the "first start" thing as documented, and you shouldn't have any surprises.

Oh. Careful especially for bridges around the VTA board. Things get tight in there and you don't want any spare leads shorting to the chassis. Also not a bad idea to insulate the PIO caps as it's easy to short the metal cases. Make sure the multi-cap is solidly mounted and well grounded too, or you could get some hummm ...

Great looking tube tester. I didn't know about this one. Thanks.

Thanks guys!
I built quite a lot of stuff over the years Heathkit, Dynakits, etc. Also, I was the Chief Engineer at the local Samsung assembly plant here in the 80's / 90's and part of that portfolio involved a lot of sample builds of new products for the production lines and some prototype work.
Have had a pretty decent electronics lab since school days. These days although semi-retired, I do a lot of Industrial and Medical Electronics consulting and Biomedical Field Support Services throughout the Caribbean.
I am really looking forward to receiving the ST-120 next week and beginning the build.

Dave_in_Va wrote:Great looking tube tester. I didn't know about this one. Thanks.

Yeah, that simple, DIY tube tester really caught my eye, especially as it can measure transconductance albeit indirectly. Glad I built it, now that I'm playing with tubes again. Came out of electronics school knowing tubes then transitioned very quickly to solid-state and microprocessor stuff (first job was Test Technician at a factory that made Ferrite-Core Computer Memory Systems here). I remember one of my first scopes was a Tektronix 545A and that thing had a ridiculous number of tubes and presented quite a thermal load on the shop A/C system..

Very nice mancave Cletus
Not the 545 but 555 but might be a fun watch for you ^^

Roy wrote:Very nice mancave Cletus  
Not the 545 but 555 but  might be a fun watch for you ^^

That certainly brought back some fond memories (I've worked on the 545 and 535) ....interesting heater regulator and power supply arrangement for that 555! .....also, our digital displays back then were Nixie Tubes and the mainframe test computer for the memory stacks we made were programmed with "punch-cards"

^^ glad you liked it Yeah I have seen those core memories around but never in person - very interesting stuff * https://www.youtube.com/watch?v=3rfCDM5olfg for those interested* I might have some punchcards here someplace - have family that worked at IBM back in the day. My mancave has a mint ibm selectric in it among other things.. Aunt of mine worked at the engineering dept. that developed it. Great for hammering out angry letters XD

Roy wrote:^^ glad you liked it    Yeah I have seen those core memories around but never in person - very interesting stuff * https://www.youtube.com/watch?v=3rfCDM5olfg for those interested*   I might have some punchcards here someplace  -  have family that worked at IBM back in the day. My mancave has a mint ibm selectric in it among other things.. Aunt of mine worked at the engineering dept. that developed it. Great for hammering out angry letters XD

Thank you, good walk down "memory" lane (pun not intended) ......I felt compelled to post a comment on that YouTube channel!

Back then is when I fell madly in love with Altec speaker systems, in particular the Voice of the Theater. I was also deeply lusting at the Bozak Concert Grand.  I eventually built a pair of Altec 620 enclosures with old but great E-604 speakers and at that time had an Oracle Delphi turntable with a Hadcock tone-arm and the Pre-Amp / Power amp was Harmon-Kardon Citation Nineteen.  About 20-years ago I built my present VOTT A7 system (not all original drivers unfortunately   ....but the sound is fabulous nonetheless) as a father-daughter project (she was six at the time  LOL), the crossovers were made by me, Alesis RA-500 power amp (my present reference), but I really like those el-cheapo Class-D amps (yeah I do ...LOL) I recently jumped-up and bought on Amazon   .....can't hardly wait to hear the ST-120 on my VOTT's.

BTW My listening area (living-room and studio) is 12' x 34', carpeted floor and acoustic tiled (fiberglass) ceiling, brick walls and the usual home furnishings therein .....the VOTT's acoustically couple into that space beautifully, the sweet-spot and the sitting-room both sound equally amazing (of course with about 6db difference between those locations).

Well, The kit has arrived safe and sound!
So the build begins here!

So this is what I did with my stepped-attenuator .....now on to painting the transformers and reading the instructions as the paint dries:

hmmm

Roy wrote:hmmm

Source A is the composite feed from my mixing/recording console preamp (avatar pic).  Source B is direct from my CD player. just tested it with my el-cheapo Class-D and it works a peach!

A little "tranny" paint going on here:

TDR Board built   ....and while the paint on the transformers continues to cure, we move on to the Driver Board (tomorrow's project)

....and the chassis gets thrown into my guitar-amp service jig  ....this thing really helps when working on a heavy yet delicate tube chassis. Comfortable work angle and good access to the 4 critical sides.