Got used Dynaco ST70 yesterday!

gnugear · Post by **gnugear** » Sun Aug 21, 2005 12:51 pm

I got a hold of a used Dynaco ST70 poweramp yesterday. Looks pretty cool for a vintage amp and it has original Mullard EL34s in it!

Does anyone know how to add a step attenuator so I can control the volume without a preamp? If I can make it work I'm going to use it for a poweramp instead of my Peavey Classic 50/50.

Flames1950 · Post by **Flames1950** » Sun Aug 21, 2005 3:09 pm

If I can make it work I'm going to use it for a poweramp instead of my Peavey Classic 50/50.

I've thought about doing that with my Dad's for years. But since I'd be using a MASS as the link between a guitar amp and the power amp/effects, the MASS line out volume would take care of the preamp aspect.
Now I just need more time to actualy DO this instead of just thinking about it......

dynaman · Post by **dynaman** » Mon Aug 22, 2005 11:42 pm

Post your question on the Dynaco-Doctor forum at Audioasylum. I'm sure it's just a matter of installing a stereo volume pot.

Don't hesitate to replace the nasty old quad cap and bias caps. And for God's sake, replace that dangerous selenium rectifier with a modern diode. Bias is set to 1.56 volts if the original resistors are present.

ST70's are by far one of the coolest looking amps out there. Post some pics

Gtr_tech · Post by **Gtr_tech** » Thu Sep 08, 2005 2:32 pm

I have a Knight "Linear Deluxe" monoblock that I had given to me years ago and the chassis is identical to the st70, with the exception of only 1 octal plug on the front, and it's got potted OT and choke. Really cool sounding amp. Did Knight just repackage Dynakit stuff or maybe have dyna make stuff for them? Bizarre.......

dynaman · Post by **dynaman** » Thu Sep 08, 2005 9:06 pm

Unless your amp uses the 7199 9-pin I'm guessing it was Knight's own design or a copy of something other than Dynaco. Dyna did make potted trannies but they're rarely seen on Dynaco amps. They usually just used the usual bell-ended design while the potted trannies were sold as single units. I think.

The Knight amps look pretty sweet too. I see quite a few of them of them on Ebay.

Flames1950 · Post by **Flames1950** » Fri Sep 09, 2005 1:08 am

Gulp......I snatched the tubes out of an old Knight stereo a few months back, and chucked the chassis in the dumpster, whoopsie.

Gtr_tech · Post by **Gtr_tech** » Fri Sep 09, 2005 12:03 pm

My Knight uses 2 12au's in the front end with a pair of p-p 5881's.
http://www.triodeel.com/knlindlx.gif
http://www.qsl.net/kb7rgg/allied/produc ... audio.html
When used for guitar with a pre in front of it the variable damping control acts as a midrange/response control. Way cool.

Flames: You pitched it transformers and all? Shame on you

Hi-fi amps usually had bulletproof iron.

I had a Fairchild 255 monoblock for years that I recently offed on Ebay. Since I only had one I really couldn't use it as it was intended to be so I figgered someone else should have it to complete a pair. It was a bit too pretty to use for guitar and the Fairchilds are a bit of a holy grail for audiophools.

Another hi-fi oddity I have is an old Magnavox console stereo amp chassis with dual p-p 6v6 cathode biased output sections. Real nice sounding, although the rectifier is getting rickety. Anyone have a 6ca4/ez81 they'd part with?

Flames1950 · Post by **Flames1950** » Fri Sep 09, 2005 6:51 pm

Flames: You pitched it transformers and all? Shame on you Hi-fi amps usually had bulletproof iron.

Yeah, the trannies were really pretty dinky for any serious guitar amp building -- especially the OT. But I scored a load of Telefunken pre's and a quad of RCA 6V6's so I wasn't too heartbroken.

That stereo did have a Telefunken 6CA4 but I might need a little $$ to grease my palms with for it........

dynaman · Post by **dynaman** » Mon Sep 26, 2005 7:47 pm

Gnugear, check these out. A must for keeping pesky fingers off the driver board.

http://cgi.ebay.com/St-70-early-style-a ... dZViewItem

gnugear · Post by **gnugear** » Tue Sep 27, 2005 1:18 am

It's true, you never see those on the amps do you?!