I'm a relative newbie to DIY'ing audio equipment, so I'm wondering if anyone has a suggestion of a nice-sounding yet simple tube amp project to get my feet wet with. 25-35 watts/channel is ideal, but aside from that, I'm open to suggestions...
Anyone?
Anyone?
Do you want to scratchbuild or rebuild?
If you have never built an amplifier from scratch, rebuilding and upgrading an existing model might be the most satisfying way to start. Some thoughts -
Dynaco ST70 - rebuild as stock & get to know it. Later, look to replace the front-end, upgrade the power supply, etc.
Generic Lafayette or Allied stereo integrated - they are on eBay all the time & usually have decent output tranformer size. Simple recapping makes a tremendous difference. Later, think about either eliminating the tone controls or making discrete PEC's to replace them.
Magnavox/RCA 6V6/6BQ5 console stereo amplifier - cheap & ugly, anything you do will be an improvement. I've heard a couple redone examples and they sounded quite nice. Recapping & power supply improvements would be the first things I'd do.
The other alternative is to build a kit. This way you'd be getting a known assuming that you buy one with a decent rep. Rebuilding an already done amplifier can be more time consuming than a kit as often part of the process is fixing the prior owner's mistake. Either way though, it is a good place to start.
If you have never built an amplifier from scratch, rebuilding and upgrading an existing model might be the most satisfying way to start. Some thoughts -
Dynaco ST70 - rebuild as stock & get to know it. Later, look to replace the front-end, upgrade the power supply, etc.
Generic Lafayette or Allied stereo integrated - they are on eBay all the time & usually have decent output tranformer size. Simple recapping makes a tremendous difference. Later, think about either eliminating the tone controls or making discrete PEC's to replace them.
Magnavox/RCA 6V6/6BQ5 console stereo amplifier - cheap & ugly, anything you do will be an improvement. I've heard a couple redone examples and they sounded quite nice. Recapping & power supply improvements would be the first things I'd do.
The other alternative is to build a kit. This way you'd be getting a known assuming that you buy one with a decent rep. Rebuilding an already done amplifier can be more time consuming than a kit as often part of the process is fixing the prior owner's mistake. Either way though, it is a good place to start.
Will approx. 8 WPC be enough? If so, check out "El Cheapo". It's low budget and a preamp is not needed.
El Cheapo Project
El Cheapo Project
Re: Do you want to scratchbuild or rebuild?
Is there anything I should look for in an old ST-70? Anything to avoid?
Thanks for the help so far. I really am a tweaky guy as my main monitoring system at the studio is a pair of B&W Nautilus 802s driven by a Pass Labs X250 and augmented by dual Velodyne DD12 subs. I want to make sure whatever I build actually sounds good as what I'm accustomed to sounds pretty good...
Excellent idea - hadn't considered that.speaker said:
Is there anything I should look for in an old ST-70? Anything to avoid?
I've searched around, but only seem to find SET with very low power - any ideas? What are some well regarded kits?
Nah, I need a good 25 minimum, I think, for normal dynamic speakers in a medium sized room.Eli Duttman said:
Looks like Greek to me - can you give me more info? Off to google...edl said:
Thanks for the help so far. I really am a tweaky guy as my main monitoring system at the studio is a pair of B&W Nautilus 802s driven by a Pass Labs X250 and augmented by dual Velodyne DD12 subs. I want to make sure whatever I build actually sounds good as what I'm accustomed to sounds pretty good...
Brad,
You didn't mention a preamp and it's always a consideration.
It's possible to extrapolate the "El Cheapo" concept from triode wired 12AQ5s to pentode wired 7591s. Costs go up considerably, but you will get 30 nice WPC. Also, it's an integrated; so, the preamp issue is already resolved.
Please keep the fact that the power to weight ratio of tube amps is less favorable than that of SS in mind. I have a TERRIFIC 60 WPC tubed amp, a H/K Cit. 2. It weighs over 70 pounds.
You didn't mention a preamp and it's always a consideration.
It's possible to extrapolate the "El Cheapo" concept from triode wired 12AQ5s to pentode wired 7591s. Costs go up considerably, but you will get 30 nice WPC. Also, it's an integrated; so, the preamp issue is already resolved.
Please keep the fact that the power to weight ratio of tube amps is less favorable than that of SS in mind. I have a TERRIFIC 60 WPC tubed amp, a H/K Cit. 2. It weighs over 70 pounds.
Likely go passive utilizing a bridged-T attenuator...Eli Duttman said:
Well, the qulaity of the power amp is most important, not the cost. Being this is a hobby piece that is likely to end up in the lounge for casual listening, it's not a requirement that it be 'The Greatest Tube Amp Ever', but I'd like for it to sound really good. Cost is secondary...
Oh, I'm aware! But I won't be lugging it around, so that's not an issue for me.
Thanks for all your help so far, guys, this place is amazing!
Any other suggestions on what I should look at?
The grid leak resistor at the I/P of the "integrated" is 100 KOhms. That mates well with 10 KOhm passive level controls. In the bargain basement configuration, a low cost Alpha Carbon pot. is used. The bridged "T" is obviously an improvement. IMO, the only place for passive level controls is inside the power amp, which makes it an "integrated". Otherwise cable capacitance can cause PROBLEMS.
The 7591 "integrated" is anything but bargain basement. It will sound GOOD, BETTER than a "mere" lounge unit. You seem willing to part with some cash. That allows you to obtain high quality O/P trafos, which are essential for superior performance. In the bargain basement "El Cheapo", steps, including bass bandwidth limiting and O/P power limiting, were taken to work around the weaknesses of the low cost O/P "iron". Better "iron" allows those sort of measures to be side stepped. The 7591 amp's bass 3 dB. down point will be approx. 17 Hz.
Sure, but I have a passive monitor controller in my mastering room and have zero issues with HF response. Just gotta be careful!Eli Duttman said:
Well, that sounds like a winner - I have no objection to an 'integrated'. Is there some place I can find a kit for this 7591 integrated or is this going to be way more involved? Is it simple enough for a relative newbie to take on?
I like automotive analogies -
Can you change a tire?
Can you change a crankshaft?
The level of difficulty for you will be somewhere in-between those extremes. That is the main reason I would recommend starting on ground that has been already trod until you get acclimated. Scratchbuilding is very rewarding or very frustrating depending on your level of expertise. Although I've never recommendend a ground-up amplifier build to someone who has never done it before, if you do decide to go that route you'll get plenty of learned advice & commentary here. In other words, you won't be out there without a net!
😉
As far as things to avoid on an ST70, the only thing I would be sure of is that both output transformers, the power transformer, & the power supply choke are good. Everything thing else is cut & paste. The amp will deliver a solid 30+ watts too. The other thing going for the Dynaco is that not only has nearly every tube afficionado in the USA had one or more, there is a myriad of parts available for it. It is the small black Chevy of the vacuum tube amplifier world. Any audio forum out there will have knowledgeable users of it. One hell of a resource base. It is nearly the equivalent of JBL in that regard.
Good Luck in your quest!
John, any experience with that amplifier? Looks too cheap to be worthwhile...
Or are there pointers/changes to be made to make it worth-while to a picky audio guy?
Or are there pointers/changes to be made to make it worth-while to a picky audio guy?
euphonicmasters said:
That was my first home-built tube amp. It sounds pretty good, actually very good for $139! If you google for 'Voltsecond' you will find a website with a lot of tweaks for that amp. I incorporated most of them in my amp and like the results.
I've since scratch-built a few more amps but still enjoy listening to that little amp with the odd tubes. 🙂
Kewl, might have to pick one of those up just to tinker with...
I've decided to go ahead and pick up an old ST-70 to rebuild/tweak on. I think that idea is the best as I get my feet wet with tons of resources out there to help me out. After that (and potentially building the little kit mentioned above) I'll be more confident to take on something more involved.
I've decided to go ahead and pick up an old ST-70 to rebuild/tweak on. I think that idea is the best as I get my feet wet with tons of resources out there to help me out. After that (and potentially building the little kit mentioned above) I'll be more confident to take on something more involved.
euphonicmasters said:
I think that is a great choice. The ST-70 is a good sounding amp. My college roommate had a Dynaco system with PAS-3x, ST-70 and FM3. He used FMI80 speakers, no longer available unfortunately, they were awesome little speakers. At the time it was the best sounding system I'd ever heard (then he took me to the place he bought it and I heard a system with a VanAlstine modded PAS, a modded ST70 and FMI J-Mods, amazing).
As you learn more and tweak things a bit the ST70 can get even better. And you are right about the resources available.
Try this
This may be a lot of fun to tinker with...28 WPC too...originally looking for a trade, but too many UCD/Tripath owner don't want to let them go...but check it out...could use a few tweaks here and there...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68588
John
This may be a lot of fun to tinker with...28 WPC too...originally looking for a trade, but too many UCD/Tripath owner don't want to let them go...but check it out...could use a few tweaks here and there...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68588
John
You might want to consider the Dynaco MKIII at 60W/ch and mono blocks. It's like a big ST-70 with bigger OT and output tubes and being mono blocks helps when you have to lift them:
http://www.geocities.com/vintageaudio/markiii.JPG
I'd go to Solid state rectifier but you MUST use some form of delay on B+ to avoid damaging the tubes, delay relays seem to make sense. Also up the B+ capacitance.
This Dynaco has the SS rectifier and delay relay, if you like this one only build it with 6550s or KT88s not 8417 outputs:
http://www.geocities.com/vintageaudio/markvi.jpg
Pete B.
http://www.geocities.com/vintageaudio/markiii.JPG
I'd go to Solid state rectifier but you MUST use some form of delay on B+ to avoid damaging the tubes, delay relays seem to make sense. Also up the B+ capacitance.
This Dynaco has the SS rectifier and delay relay, if you like this one only build it with 6550s or KT88s not 8417 outputs:
http://www.geocities.com/vintageaudio/markvi.jpg
Pete B.
euphonicmasters said:
- Status
- Not open for further replies.