The trouble with that plan is that I'd eventually end up replacing virtually everything, either for performance or for looks. I don't see much there of value, considering the price they typically sell for. So I think it would end up being a waste of money.
Taj,
6BG6GA's "moniker" provides a good hint.Check dad's caddy for that type. It's easy enough to make a 30 WPC variant on the Cit. 5 around it. Canada made Hammond 1650P O/P trafos will do quite nicely.
I'm getting really curious about the contents of that caddy.
..Todd
I'd further suggest going Mk.IV-style and building monoblocks. ... Build their PS like it should serve a stereo amp...
Douglas
Not sure I understand the difference if the power supply was serving both channels. You mean use separate input PCBs for each channel? Please elaborate.
..Todd
Quote:
Which one would you say is the best and why? or better...
How would you describe their differences?
I have the following driver boards
1. Stock Dynaco stereo 70 with 1% resistors and premium caps
2. Mapletree Board
3. A modified hand built Mapletree design
4 . Triode Electronics 6AU6/12AU7 board
5. Kevin Kennedy board from Geek
6. Geek octal 6SL7/6SN7 board
How would I describe their differences? Well, they are all different thats for sure. If I were to rate them it would be hard and I'm still in the process of listening and every time I think I am close to making a decision I think that I just heard something new and different that I didn't notice before. I can tell you for certain that the dynaco board with the 7199's sounded better with matched premium parts. It was out done however with all of the other boards.
I have enjoyed all the boards so far. There is so much that can be improved upon with this somewhat basic amplifier.
My personal opinion on the output transformers is they are good and I do believe it would probably cost twice as much as a run of the mill Dynaco cost to obtain transformers that would provide a increase in performance that could be heard easily by the average person. The chassis is usually junk or close to it. The power transformer is usable as is. I do have one unit with the replacement transformer that has larger filament capabilities and runs cooler.
Never had a power transformer burn up yet. Yes, they will support the filament requirements of some of the newer driver boards running something other than 7199's.
Which one would you say is the best and why? or better...
How would you describe their differences?
I have the following driver boards
1. Stock Dynaco stereo 70 with 1% resistors and premium caps
2. Mapletree Board
3. A modified hand built Mapletree design
4 . Triode Electronics 6AU6/12AU7 board
5. Kevin Kennedy board from Geek
6. Geek octal 6SL7/6SN7 board
How would I describe their differences? Well, they are all different thats for sure. If I were to rate them it would be hard and I'm still in the process of listening and every time I think I am close to making a decision I think that I just heard something new and different that I didn't notice before. I can tell you for certain that the dynaco board with the 7199's sounded better with matched premium parts. It was out done however with all of the other boards.
I have enjoyed all the boards so far. There is so much that can be improved upon with this somewhat basic amplifier.
My personal opinion on the output transformers is they are good and I do believe it would probably cost twice as much as a run of the mill Dynaco cost to obtain transformers that would provide a increase in performance that could be heard easily by the average person. The chassis is usually junk or close to it. The power transformer is usable as is. I do have one unit with the replacement transformer that has larger filament capabilities and runs cooler.
Never had a power transformer burn up yet. Yes, they will support the filament requirements of some of the newer driver boards running something other than 7199's.
I've reached the same conclusion. The chassis that you find are usually rusty/pitted, the 7199 driver is obsolete, and many folks upgrade the power transformer since it's marginal, as well as the tube sockets, caps, input connectors, and speaker connectors if you want modern 5-way binding posts.
That leaves the output transformers. So it makes sense to me to buy some nice output transformers with the money saved from not starting with an old ST-70.
Hey Geek,
When you designed the DynaMutt, what were your goals? You described what you did in terms of technical details, but not really what made you decide to do it the way you did. What led you in that direction?
Hmm.. Maybe a better way to pose my question would be ask how a DynaMutt differs from the other ST-70 boards kicking around the internet. I guess I'm prodding for a bit of a sales pitch.
..Todd
When you designed the DynaMutt, what were your goals? You described what you did in terms of technical details, but not really what made you decide to do it the way you did. What led you in that direction?
Hmm.. Maybe a better way to pose my question would be ask how a DynaMutt differs from the other ST-70 boards kicking around the internet. I guess I'm prodding for a bit of a sales pitch.
..Todd
Hi Taj,
The main design goals were:
- Get away from the 12A_7 rut.
- Tube selection with equal sonics and performance in octal or noval versions.
- Tube cost effectiveness: No need to hunt for a PI tube with perfectly matched sections (which 6CG/FQ7's rarely have).
- Real AC and DC balance off the PI: Nothing forced.
- Be able to use 5% resistors with no performance loss over 0.1% geewhizbang types.
- Stability: No HF compensation required (like the R/C network or 390pF UL FB cap on the original PC-3 design)
Cheers!
The main design goals were:
- Get away from the 12A_7 rut.
- Tube selection with equal sonics and performance in octal or noval versions.
- Tube cost effectiveness: No need to hunt for a PI tube with perfectly matched sections (which 6CG/FQ7's rarely have).
- Real AC and DC balance off the PI: Nothing forced.
- Be able to use 5% resistors with no performance loss over 0.1% geewhizbang types.
- Stability: No HF compensation required (like the R/C network or 390pF UL FB cap on the original PC-3 design)
Cheers!
quote:
6b, do you have the Geek octal 6SL7/6SN7 board running already?
THe board is complete and I am 1/2 way in wiring it in. I have high hopes for
this board.
Quote:
Originally Posted by taj
The trouble with that plan is that I'd eventually end up replacing virtually everything, either for performance or for looks. I don't see much there of value, considering the price they typically sell for. So I think it would end up being a waste of money.
If you are really interested in one I would sell you a turn key unit. Has new transformers (all) New Mapletree Driver board, new power supply board, has had the chassis stripped and re-chromed, not nickle. Everything is new
Typically you can get a 70 for around $200-250 shipped. Cheaper if you run into a garage sale piece.
I think there is too much ** about the transformer being marginal. It will run the 70 plus a preamp off its power supply without a problem. I will admit that I was worried about the transformer temp but have monitored it and found it to be ok. It will run the filament demands of other boards running (2) 6SJ7's and (2) 6SL7's or (3) 6sn7's or (3) 12AT7's without a problem. In my opinion $200-250 for a pair of output transformers and a power transformer isn't too bad. Wouldn't you expect to replace sockets and power supply caps in a 50 yr old piece? I would.. Heck you can sell the transformer on eblay for over $60 without a problem.
I guess maybe it boils down to how good you are and the time you wish to spend on a project. I have seen 70's having had their chassis glass beaded and epoxy painted or re plated. If you are handy you can build a chassis yourself.
6b, do you have the Geek octal 6SL7/6SN7 board running already?
THe board is complete and I am 1/2 way in wiring it in. I have high hopes for
this board.
Quote:
Originally Posted by taj
The trouble with that plan is that I'd eventually end up replacing virtually everything, either for performance or for looks. I don't see much there of value, considering the price they typically sell for. So I think it would end up being a waste of money.
If you are really interested in one I would sell you a turn key unit. Has new transformers (all) New Mapletree Driver board, new power supply board, has had the chassis stripped and re-chromed, not nickle. Everything is new
Typically you can get a 70 for around $200-250 shipped. Cheaper if you run into a garage sale piece.
I think there is too much ** about the transformer being marginal. It will run the 70 plus a preamp off its power supply without a problem. I will admit that I was worried about the transformer temp but have monitored it and found it to be ok. It will run the filament demands of other boards running (2) 6SJ7's and (2) 6SL7's or (3) 6sn7's or (3) 12AT7's without a problem. In my opinion $200-250 for a pair of output transformers and a power transformer isn't too bad. Wouldn't you expect to replace sockets and power supply caps in a 50 yr old piece? I would.. Heck you can sell the transformer on eblay for over $60 without a problem.
I guess maybe it boils down to how good you are and the time you wish to spend on a project. I have seen 70's having had their chassis glass beaded and epoxy painted or re plated. If you are handy you can build a chassis yourself.
Are you having problems getting yours going, Tom? Help's just an email away!
Cheers!
I'm good, waiting on some Edcors...
I'll second everything 6bg6ga just said. Initially I was gonna build an amp from scratch (still will eventually), but I already rebuilt one ST70 and now starting on another. One thing old age has taught me, to satisfy myself I have to learn and do a few times or I'll always have remorse about "wow, if I could just do that over, I'd be so much happier with it".
Well, needless to say I am doing several things (to the better) on my second ST70 that I did not do on the first. And I already have ideas how to improve the next amp. And by improvements I mean how to put it together, components used, appearance, etc. not to mention better driver boards (like Geek's) that come along. What I'm trying to say is this, if you have time to build your own amp, make time to practice on a couple of ones that you know won't be your "ultimate amp" first. The experiences will make your "ultimate amp" be so much better when you get to building it.
As far as money is concerned, if you buy an old ST70 reasonably and redo it, you should not lose any money if you sell it, and even if you "lose" a little, so what, what you've gained in knowledge is well worth it, in my opinion.
Wow! I've never seen one selling for less than about $400 (FOB seller) -- even dead. I've been watching eBay (on and off) for a couple years now. Prices there are pretty consistent. If you bump into one at $200, please let me know. In that case I agree completely, and I would not hesitate to buy one for a project like this (assuming it's not a complete rust-out). But I think you're pretty optimistic with that price.
Maybe I'm looking in the wrong places (?)
..Todd
Last edited:
I just bought one this past weekend for $300 shipped off ebay.
Dynakit ST-70 Philly Classic- Working / Restorable - eBay (item 220537347231 end time Jan-08-10 15:28:03 PST)
In Sept, I got one that was missing tubes and not guaranteed to work for $185 shipped, it too had the cage but the transformer was bad. I put a new driver board in it (VTA board), found a used transformer, since sold on ebay.
In all cases (and a couple of pieces of broken McIntosh gear) I also got since Sept. (and since resold after fixing--solid state amps), I ALWAYS used BIN to get what I considered a better deal than bidding against others. But, I am retired and probably look too much on ebay and you have to act quick before others see it. Unfortunately, if I saw another ST70 today for $200 or $250 BIN, I'd buy it...sorry Taj.
Finally, you will hear of the thrift store or garage sale, or estate sale find for a buck-ninety-eight. However, I've never seen anything in the local Goodwill and I don't want to go to estate or garage sales so have to pay more on ebay, I'm sure.
Dynakit ST-70 Philly Classic- Working / Restorable - eBay (item 220537347231 end time Jan-08-10 15:28:03 PST)
In Sept, I got one that was missing tubes and not guaranteed to work for $185 shipped, it too had the cage but the transformer was bad. I put a new driver board in it (VTA board), found a used transformer, since sold on ebay.
In all cases (and a couple of pieces of broken McIntosh gear) I also got since Sept. (and since resold after fixing--solid state amps), I ALWAYS used BIN to get what I considered a better deal than bidding against others. But, I am retired and probably look too much on ebay and you have to act quick before others see it. Unfortunately, if I saw another ST70 today for $200 or $250 BIN, I'd buy it...sorry Taj.
Finally, you will hear of the thrift store or garage sale, or estate sale find for a buck-ninety-eight. However, I've never seen anything in the local Goodwill and I don't want to go to estate or garage sales so have to pay more on ebay, I'm sure.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.