Audio Asylum Thread Printer
Get a view of an entire thread on one page
|For Sale Ads|
Hi, got a pair of these boards off eBay that converts the 7199 to 6GH8, however, no installation instructions even after contacting the vendor! Does anyone have experience with these boards and how to hook them up to Dave's EFB+? I know I should have bought Dave's replacement boards but wanted a stuffed board ready to go. Thanks!
Spending a few extra bucks and buying the board from the "REAL" designer pays for itself in two ways.
Most importantly you have support from the seller/designer. Besides the vast pool of knowledge of those that have used, tweaked and modified those boards - with success!!!
Don't support ebay. Support those that have taken the time, effort and true love of building these boards - the right way.
I've said my piece and now I'll move out of the way.
Charles, tubes4hifi sold many a VTA70 board on Ebay. Also, I've seen the Bob Latino sell his kits there as well.
Yes, but they are the original designers selling THEIR products. Not a knockoff.
That was my poorly phrased point. Compensate the people that DID the work.
But if Dave Gillespie was selling his boards, or Jim McShane were selling tubes on ebay I wouldn't hesitate to buy from either one of them.
You do have to know what you're doing though, and buying these boards in question from a Chinese seller is a risk. As gkargeen found out, there's little to no support offered, and as I speculated in another reply, there's the likely potential for counterfeit components to be installed.
Still, for some who don't have the soldering skills, or are in a rush, the Chinese products prove to be too tempting to resist.
So, where ebay is concerned, you're certainly correct in cautioning, "Caveat Emptor"
I am not like most people whose posts I have read here. While not quite up there with Dave, Eli, Mikey, etc., I do know my way around a circuit and which end of a soldering iron to hold. My main issue with these boards was that they moved the balance control input position, once I checked the circuitry I figured out what had been done and how to properly use these boards, which I feel are fine products, maybe not as good as Dave's, but not some piece of shit either, I could see that from the pics on ebay. To dismiss ebay as some junk shop of parts is extremely ignorant, I have bought and sold many pieces with no issues at all, and that includes Chinese and Russian parts. Caveat Emptor is certainly valid in ANY dealings in life, particularly with businesses as a customer (oh how they screw us!) to being an employee of most businesses. That doesn't mean you don't use one, just use caution.
I'm sorry if you felt put upon by my post.
Some of my impressions of the quality of the (and the risk of counterfeit) components, on these Chinese ebay boards came from a post on the Tube DIY Asylum which I read about five years ago (link below) where the poster said he had to replace all the capacitors which his ST-35 boards came stuffed with to get it to sound good.
As for dismissing ebay as "some junk shop", I wasn't the one who did that, but you're implying it by saying it in your reply to me. To repeat what I said, ebay can be fine to purchase from, but one has to use caution, know what they're buying, and who they're buying it from.
That said, I'm glad you got your issue sorted out.
shovel, I wasn't totally throwing you under the bus here, that post was mostly directed towards airtime, who has this habit on AA of making comments with little technological reasons to back it, i.e., uninformed responses. You, OTOH, had something solid to offer (although you did come off a bit strong on the anti-ebay thing) an that is appreciated. There was a post that was deleted by airtime right after posting that was incredibly, ah, less than attractive, he realized that and quickly removed it to his credit. In my two previous rebuilds I rebuilt the PC10 boards and believe them to be better than these new boards due to component quality, that being said, these boards are not junk and I would use them again if pressed. Dave's boards I believe are a better design and would go that route first, I can also control parts quality. The costs would be the same, but stuffing the boards would add several more hours to the project and thus cut into my profit on these repairs/restorations, which is something I need to keep in mind. Thanks!
Hi, post a link to the auction and i'll have a look. It should be doable. I think that I read though that a tube sub in a sca35 doesn't work well without a circuit tweak where in a st70 it's pretty much a socket rewire.
Thanks, Danny, I talked with Dave G. and have pretty much figured out know how those boards are to be connected.
Great. Dave is a really nice friendly guy. I did a Fisher 400 with his tweaks and it's one of my favs. I'm sure that your SCA35 will deliver. Let us know how it turns out.
Yes, Dave has been a real quality person that is unstinting in his help to others, that is why I have already bought and installed 3 of his EFB+ boards in various SCA35 rebuilds. In the first two I had good 7199s so I rebuilt the original boards with all new parts and sockets. This most recent rebuild was missing the 7199s so I decided to use a prestuffed board to get the project done quickly, little did I know the issues that have cropped up, but, with Dave's help, have been resolved. In the future, if I need new PC10 boards I will just buy them from Dave and stuff them, that in the end will save me time.
Great. I'm glad that you got it sorted. I figured as long as the board wasn't too far off from the original design you'd be good. Good luck with the rest of the rebuild.
IIRC, no parts value changes are associated with the switch from 7199 to 6GH8. In addition to what other posters have stated, look at the original, for how things get wired up.
In general, you certainly may be right, Eli. But as noted in Gillespie's installation manual (copied and pasted below), that may not be the case with the SCA-35. That's one reason I suggested the original poster refer to Gillespie's guide when installing his boards.
"10K resistors - why are these necessary?
While, in many amplifiers, a 6GH8A or 6U8A will perform well as a replacement for the 7199, this is not always the case with the SCA-35. The bias and feedback circuit is somewhat unique, and specifically suited to "original" 7199 tubes. The 10K resistors are installed in place of jumper wires on the bottom side of the PC-10A. These are necessary because the 6GH8A or 6U8A are not exact replacements for the original 7199. The resistors will prevent instability issues which may occur as the amplifier is just driven into clipping. As well, additional phase shift components are included on the PC-10A to prevent spurious oscillations which may otherwise appear in some cases when using a 6GH8A or 6U8A."
Whether or not these "additional phase shift components" on Gillespie's boards are installed on the original poster's Chinese boards is something he should have investigated in advance, not to mention the likelihood of counterfeit components being used on his ebay boards.
I wasn't aware that Dave had these boards available for the SCA-35, so I thank the original poster for inadvertently making me aware of that. That way I'll have two more 7199 tubes to add to the precious few I have to keep on one of my stock ST-70s running a little longer.
Since the ebay seller probably ripped-off Dave's board design anyway, maybe you can use Dave's installation guide as a...wait for it...guide. I'm not suggesting to follow it exactly, 'cause I don't know if the boards you bought are exactly the same. But since what you bought didn't come with instructions, that's where I'd start, looking for any differences between Dave's instructions and the boards you have during the hook-up.
Thanks, shovel, that is kind of the way I am thinking of going, even though the boards are not quite the same as Dave's design...
You never said which ebay seller you bought your boards from, but in doing a search, I found the ebay seller linked below. Is that where you got yours?
If so, you're right, they do differ from Gellespie's circuit. I only count 9 resistors on the ebay board (same as a stock SCA-35), while Dave's board contains 10 (eleven, if you count the 10K which goes between V-8 pin #2 and eyelet #8, which he adds underneath). Also, I only see the stock Dynaco circuit 12pF cap, no additional (C1) 18pF, as on Dave's board.
If it were me and I had already purchased the stuffed ebay boards, I'd try and shoehorn in the 18pF @500V C1 cap and R38 100k 0.5W resistor missing from the Chinese (i.e. otherwise stock) circuit, as well as using the 10K 0.5W Dave recommends.
Also note that Dave has increased the value of C18, which was 0.1uF @ 250V on the stock board to 1uF @ 250V in his circuit.
Good luck with your project.
Thanks, shovel, that is exactly the boards I bought, I am guessing they are based on another design, not Dave's!
I don't why this Asylum is obscured anymore but all things dynaco can be found here.
Try cross posting this over at the tube forum. If not try the audiokarma tube forum or a dynaco forum.
Did you at least get a schematic? If so you may have to figure it out from that.
Post a Message!
This post is made possible by the generous support of people like you and our sponsors: