by the time you swap those around again, they may be heat damaged.
I hope to put my own amp on the bench this weekend but I've got a couple of customer preamps to get built and finished first.

This is what i've been told to do:


With your generator plugged into yourpreamp.



The feedback disconnected on the amp.



Using your pre to balance the output onpin 1 and 6 of the center tube with your scope.



--



Then check the output at the 8ohm taps tosee if it’s even.



If it’s even you know it’sstill in the first section if you had to balance it with your pre.



If it’s not even then check pin 5 onthe output tubes to see if it’s even output between

channels, if it’s higher on 1 thenit’s either the CCS or the tubes in there as well.



----------------------



Disconnecting the feedback an making iteven at the center tube with your pre(checking with the scope on pins 1 and 6)



Then checking the rest of the amp willtell you where any issues are.

if you try that, obviously you'll want to be using test loads, not speakers, so 8-10 ohm resistors rated at 50 watts.
Also don't forget you'll have about 4-5X as much gain (12-15db) of gain with the NFB disconnected.

Won't the preamp prevent speaker damage?

NO!! Remember....the signal is still going through your output transformers!! They need to be hooked up to a load.....and doing this with dummy loads is a good idea, since you eliminate the reverse emf and impedance fluctuations from a working speaker. So, if you don't have dummy loads......get some! As I think 'Roy' said, an 8 to 10 ohm resistor at 50 watts is good......but two 15 to 20 ohm resistors at 50 watts each, then in Parallel is better! Or, a good 8 ohm Dummy Load from Parts Express is the best way to go. I think they sell non-inductive 100 Watt dummy loads wrapped in heat-sink aluminum for about $10 each. I think I bought a pair of 8 ohm versions about 15 years ago....and 4 ohm versions a few years back. Money well spent.

Tom

I think I have it figured it out. A back and forth with Kegger over the phone lead to the discovery. With the feedback reconnected, preamp, scope and function generator running I balanced the VTA tubes with the balance pot on the preamp and scope so the output was equal on both sides- 8 ohm taps still showed a large difference between output signal which lead to investigation of the outputs. Screen and plate to center tap ohmed out even on both sides. The signal on the plate on one set of tubes was off the map, the other was normal. Screen to plate on one side reads ~180 ohms, the other ~80 ohms. Issue is the screen to plate winding on the one transformer, it is 100ohms higher than it should be, in mine and Kegger's mind, it's a manufacture defect. I need to call edcor and give em hell!!!

yeah, not at all related to the board itself, you've either got the transformers connected wrong, or more likely,
Edcor sent you a messed up pair

The transformers aren't connected to the tube sockets anymore, they are measuring this way stand alone.

Gee.....if ever there was a time for an 'Eytolyaso' maybe this would be it?......lol

Funny how the things ya just don't think could possible be so....turn out to be so!

Anyway.....glad you got it sorted out. Like I said, I've been through this kind of bugger.....and it took me nearly 2 weeks to finally do the obvious and check the primary windings on the Fisher amp. After some back and forth with Heyboer, I finally got a new matched pair for that amp....but in the interim I had acquired a 'used' set that, although un-matched with one being from an X-100 and the other being from a 400, both work beautifully in the amp. I think I mentioned that I also had to shoe-horn a 400 power transformer into that amp as well. So, it's a few pounds of iron heavier than it should be.....but certainly sounds good!

Anyway....I'll be interested to hear how Edcor treats you about 'fixing' this transformer. I think you mentioned that didn't buy them 'new'.....so perhaps the guarantee is a 'first owner' kind of thing? Wouldn't surprise me! But, perhaps they'll be 'big' about it and help you out....even if its just partially. I think you'd have to agree that even that would be 'fair'.

Glad you've made some progress!

Tom

It's all fixed, edcor miswired the pair of primaries for the tubes, it's wired blue brown stripe - brown blue stripe and is perfect now.

Your telling me and then on top of that the customer service dept told me it would be 3 weeks after I return it on my dime that they would send out a replacement. They do not stock ANY transformers, it is a one off company. Time to do some checking on Hammond to see if they are any better.

In their defence, for the price they do sound good.

bktheking wrote:Your telling me and then on top of that the customer service dept told me it would be 3 weeks after I return it on my dime that they would send out a replacement. They do not stock ANY transformers, it is a one off company. Time to do some checking on Hammond to see if they are any better.

In their defence, for the price they do sound good.

Being a manufacturer's representative of commercial audio and video products, I would consider Edcor's response inadequate. While they are free to set their own policies, they are still shirking their responsibility. If you plan to return the defective transformer, you should insist that Edcor sends you a "call tag" for pick-up by their preferred carrier (FEDEX or UPS). In addition you could also ask for an advance replacement, returning the defective product afterwards. Most manufacturers are anxious to please their customers (although there are exceptions), especally when the issue is a manufacturing defect. They certainly have an ethical obligation to do so.

Best Regards,
Charlie

I too also thought that was the norm, an advanced replacement policy similar too most companies. In speaking with their technical support rep on the phone I asked if what I was seeing was normal and then asked when I'd see a replacement. He told me he "has never heard of it" and that if it were a fault of theirs (which it clearly was, i'm not a crackhead) my transformer would be at the "front of the line". In other words, sorry we screwed up building it but we don't have replacements. His excuse was that in order to keep their prices low they kept no stock. When I asked if they had replacements for defective transformers I was told no as there are just too many variables. You have a product line that offers "standard" PP transformers , this wasn't a custom transformer with windings I came up with, it was one off of their website. I guess Edcor has interest in making customers wait while they sell transformers at a lower price. I'd rather pay a little more and get the support if they "screwed up" vs waiting a month to get a replacement cause they don't have stock. If I get into the biz of building these st-70's I'll make sure I get good support on all facets of the build. Bob and Roy are great, that's why they get my money on the board side. Needless to say it's one of those "you get what you pay for" statements. I'm just glad I figured out how they wired it instead of having to wait for a replacement.

In all honesty when I spoke to the 2 reps at Edcor it sounded like I was calling a sweat shop. I've been in the IT business for close to 16 years and have dealt with darn near every manufacturer in the IT world- everything from Novell and Microsoft to Dell IBM and HP and never have I been spoke to with such "I don't really care about your issues" attitude. I couldn't make this stuff up if I tried.

I'm going to play Devil's Advocate for a moment and stick up for Edcor for just a bit! I spent over a decade as a "Customer Relations Manager" for a major US Automotive Manufacturer in Detroit, so I've got a bit of experience in this area! I'm not saying BT is out of line here, but Customer expectations 'can' run AWFUL high....and sometimes be unreasonable. As a large business....we generally would confirm a defect prior to making ANY type of commitment, and most certainly so outside the warranty period. And, just as a quick 'aside'....the term 'defect' has a LOT of open space in it. But, it's generally defined as: That which fails within the term of the warranty. Beyond that, it's simply a failure; albeit materials, workmanship, or even design. But, manufacturers are VERY specific about, what, how, and when they cover these failures, and when they don't. Further, they generally EXCLUDE things like 'damage', 'misuse', or 'abuse'....even when a product is within the warranty period. If I'm not mistaken.....BT's OT was not purchased by him 'new', which is also most generally another stipulation that most manufacturer's put on their 'warranty'. Generally, a 'warranty' related repair will ONLY be afforded to an original owner unless the product specifically comes with coverage based only on time from original purchase.

As we've all been in the 'electronics world' for a while, we all know how easy it is to make a simple mistake and see something go 'poof'! So....again, from a manufacturer's perspective.....and in a SMALL COMPANY at that....the idea that they would be willing to look at a 'used' transformer and cover it to a 'second owner' after simply wanting to confirm a mis-build....to me is VERY GOOD policy! Granted, there may be a time-lag involved, but very few companies will send parts in advance.....and frankly, I know of none! I can't conceive that Bob or Roy would send out another board without having their old one back first.....but maybe! If so, GREAT! But most companies need their product back to be able to confirm responsibility....OR...get one of their vendors involved in the cost of replacement/repair! 'Vendor Recovery' is another HUGE part of Warranty Cost Administration!!......I know.....I did this job for another 10 years as well!!

So......having said all that....I know the frustration of being faced with a 'bum' part......or getting 'bad service'! Clearly, it appears Edcor screwed up! But, sounds to me like they were trying to offer a way to make it right! Granted, some postal costs may have been involved......but again....I find that pretty 'normal'! It's great that BT was able to 'fix' this on his own.....my last experience did not turn out quite as well. I had to get another whole OT made.....but 'my manufacturer' made good on replacing the bad one at N/C (except postage) and cut me a good deal on a matching unit so I'd have a 'pair' for my next build! Honestly, that delighted me! But, from a 'time' perspective, the 'fix' took nearly 2 months....so consider that when looking at Edcor's 2 weeks or so!

Anyway.......two sides to this! We all tend to think from a customer's perspective, and rightfully so! But trust me, if these were made in Asia or elsewhere, you'd NEVER get anything done about the problem!! Suddenly what ever English was used to make the purchase, it would disappear when it came to sorting out a problem!! Just went through that mess too.....and I'll keep ALL my business here in the USA if I possibly can! Edcor has a pretty good reputation for performance.....maybe their Cust. Relations practices aren't so good.....but I'm guessing if they grow and continue to be a viable company here in the US, they'll get better. So, I hope my 'support' of them is not misplaced!! I'd like to try a set of their transformers some time.....and I'm really anxious to hear how BT feels about these units after he has a chance to listen to them for a while.

Again........good luck!!

Tom D.