edwardre Posted September 28, 2002 Share Posted September 28, 2002 Just about finished with the ST70/PAS upgrades. I understand that most caps (I've replaced all with 'orange drops') take some time to break in. However, I'm noticing that the Tesla tubes I'm currently running are a bit on the 'harsh' side. WRT the easily available tubes....JJ/Teslas, Sovteks, or Svet's, which should provide the best overall tone? Should I 'wait out' the cap break-in period first? Will I notice a significant change as the caps break-in? Finally, originally I had Mullards. Probably never obtain the same sound with the abovementioned tubes. The problem with the Mullards is I busted one so now I have 3. Would it be sacriligious to use 3 Mullards and one JJ? Would this combo still sound better than 4 JJ's? I'm a little apprehensive to just experiment as I've blown it in the past...... Quote Link to comment Share on other sites More sharing options...
Deang Posted September 28, 2002 Share Posted September 28, 2002 I'm betting the new parts are contributing more to the "harshness" more than any tube could do. JJ/Tesla has a good reputation. You should wait it out. How many hours on the Teslas? Tubes also need about a 100 hours to sound their best. I we are talking power tubes here in a push-pull amp, you probably don't want to mix up the tubes. How old are the 3 Mullards? Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted September 28, 2002 Share Posted September 28, 2002 Many in here dont agree with breakin but I do. I have heard the results too many times to discount and it is far more than your ear/brain getting used to the sonics, although this does play into the equation. Although I have back it in the past, I would opt for caps like the Orange Drop 716p only if you need the space or are tight with the funds. Frankly, I think there are better caps out there that are smoother; the 716p can sound a bit brighter. Running them in should help some but be warned that there are better options for something like the ST-70. No, I would say that you cant get much better than the Mullard EL-34. But in some amps, I have found the Svetlana EL-34 do pretty well. I have never liked Sovtek EL-34 so at least you arent saddled with them. Some like the JJ but I see more liking the Svetlana in the ST-70. NOS DOES indeed sound better, however. I would personally wait a bit and let the amp settle in as well as you getting used to it before going with too many options yet. Quote Link to comment Share on other sites More sharing options...
Guy Landau Posted September 29, 2002 Share Posted September 29, 2002 Ed, Test your Mullard tubes on a tube tester and if they atill test strong,try to buy a matching 4th tube on ebay. There's a manufacturing code near the base of the tubes starting with xf... What is the code on your mullards? Quote Link to comment Share on other sites More sharing options...
Deang Posted September 29, 2002 Share Posted September 29, 2002 That was my thinking as well, which is why I asked him how old the Mullards were. I was thinking it might be easier for him to get a match if they towards the end of their life. Kelly is right about the Svetlanas. I run their KT-88's, and I'm very happy with the sound. Seems several on this forum bear striking resemblances to each other:) Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted September 29, 2002 Share Posted September 29, 2002 You may want to retrofit the DT-70 with bias controls for the output tubes. I am planning to do this with my various projects. Then you have better control. This brings up a question: what happens if your output tubes are not matched? How does this effect the sonics? From what I understand, and I am a relative newbie at this, you can have two possible controls for each set of output tubes, one for the amount of voltage applied to the plates, and one for the balance. Some amps come with a balance control built in, and others do not. If you do not have the controls you need to put in tubes that are "matched". If I am not mistaken, these tubes can drift over time and loose their match, thus requiring renewed tweaking. I too am just learning about all this, so any pointers or info will be helpful. -C&S Quote Link to comment Share on other sites More sharing options...
NOSValves Posted September 29, 2002 Share Posted September 29, 2002 Klipped, The advantage of having complete bias control isn't just that you don't need balanced tubes. The fact of the matter is that there is no such thing as a matched set of tubes period. I have a tester and have played with the bias alot and found that while when you have bias control a matched set of tubes are easier to bias they still are never a perfect matched set or quad ! I have used tubes that match within .02 percent of each other and to achieve the same current draw on these tubes one might require 1 to 2V more or less bias voltage to even them out. The sonic difference is small but it is there. The draw back to a completely non biasable amp is that tubes don't last because they are never operating optimally period mark. This matching is for the most part a joke. It does help but isn't all they crack it up to be ! I myself wouldn't own a amp that doesn't have at least a single bias voltage pot and a balance pot per channel. Ideally dual pots of voltage and balance is the way I go. Now if your a person that is scared to get inside a amp to bias it then its really not worth adding ! Craig Quote Link to comment Share on other sites More sharing options...
edwardre Posted September 30, 2002 Author Share Posted September 30, 2002 Thanks all for the input. Dean - the JJ's have maybe 10 hours on them Purchased as a matched quad from Triode awhile back. The Mullards are at least 25 years old. When I had them tested a year or so ago, they were still good and fairly 'matched'. Mobile - I 'upgraded' to the Orange Drops only because they were readily available and I had read that they are tonally desireable. They seem bright to me but I will certainly wait and put a few hundred hours on them before deciding upon more 'tweaks'. What type(s), in your opinion, are a better fit? Guy - I did not check the mfg code, but will tonight. They have a dark brownish base and I believe that they have single 'halos'. I have been scoping the bay for a few days now, but man, those Mullards are in demand! C&S/NOS - As you probably know, the ST-70 has a single adjustable bias pot per channel. I'm very new to this audio field, but would either of you know if this pot is sufficient or should I start looking around to add another? The adjustment is to adjust some voltage to 1.56V on each channel. With this in mind, when I do adjust each to 1.56V, am I 'balancing' out inequities in the tubes? Thanks! Quote Link to comment Share on other sites More sharing options...
leok Posted September 30, 2002 Share Posted September 30, 2002 edwardre, Tubes in the initial gain, phase split, and driver circuits have significant impact on the sound. I don't know what your amp uses, but I've found that NOS Philips and Mullard are good for E88CC. An RCA 6922 (same as E88CC), made by Seimens, seemed to distort the high end (I think that's what people call harsh). Good NOS miniature tubes are not too expensive, but, if you want, I think you can still buy a particular E88CC pair for $500. leok Quote Link to comment Share on other sites More sharing options...
k2dx Posted September 30, 2002 Share Posted September 30, 2002 Hey Ed! Good to see you're digging into the st70. Adjusting the bias should be done measuring the idling current through the tube or pair of tubes being set. This probably is done indirectly by measuring a voltage drop across a resistor. I think some amps had a jack you could insert a milliampmeter in line directly to measure the current. Measuring the voltage drop across a resistor will also give you the current using Ohm's law, I=E/R. The best way to set bias would be to have a pot for each output tube, then you wouldn't need to "match" tubes in a pair. But you don't want to mix tube brands in a pair. The idling current sets the class of operation for the tube...class A highest idling current,least efficiency,less power, best sound. Less idling current for class AB, more power and higher efficiency, but sound not as good as class A. Your amp probably calls for class AB1 or AB2 settings being a push pull. Maybe on Audio Asylum, Tube Forum, someone could give you specific advice on the st70. I don't think 715 or 716 caps would be my choice. Quote Link to comment Share on other sites More sharing options...
edwardre Posted October 1, 2002 Author Share Posted October 1, 2002 Hi Fred, thanks for the input. You're the 2nd person who has said that 715/716's wouldn't be their first choice. However, I've read that they are suppose to be a good 'upgrade'. Would be interested in hearing your reasons for not using? What would be a good substitute? WRT tubes, think I'll just wait it out and try and score a Mullard from e-pay to match the 3 I have. Thanks! Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted October 1, 2002 Share Posted October 1, 2002 I have gone on recording recommending the Orange Drop 716p (not the 715 which has copper clad steel connectors) several times, especially in vintage upgrades where space is at a premium. It is an OK cap and costs practically nothing compared to some of the big names. It's a polypropylene and foil cap which is better than metalized poly. But I dont think this cap matches the sonics of some others and can sound slightly hard compared to others. Steve at Angela says the caps might sound slightly brighter due to the hard coating SBE uses. I love the Jensen Copper Foil Oil caps and have them in my 2A3 amps at the coupling positions. They are too expensive to throw everywhere but in critical positions, and if you have the room, they are EXTREMELY sweet and musical, offering the antithesis of HARD sound - they are both liquid and highly resolving, a rare combination. They dont have the snap of something like a MIT RTX or Hovland but sound more natural and real to me. Others have been happy with the Auricaps and they are a relatively cheap alternative. They arent Jensen or Audio Note.... Let your amp break in a bit more and see how it goes. You might end up wanting to replace those 716p later. Quote Link to comment Share on other sites More sharing options...
edwardre Posted October 2, 2002 Author Share Posted October 2, 2002 Yeah, that was my thought.....let the new sound soak in for awhile then adjust my thinking accordingly. Are the leads the only thing different between the 716p's and the 715's? I don't think mine have either identifier on them. How would I know what I have? Thanks! Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted October 2, 2002 Share Posted October 2, 2002 Edwarde, see this page: CAPACITORS - Selections/Explanations There are pics of the 715 and 716. They should have a label on them with the numbers as shown. Be sure to read on down that page for some interesting cap comments. I am still surprised if you went for Solen FAst Caps as your coupling caps. These are really more for power supply / speaker crossover work. PErhaps you didnt mean you got them for coupling. kh systems Quote Link to comment Share on other sites More sharing options...
edwardre Posted October 2, 2002 Author Share Posted October 2, 2002 Yes, MH....regrettably I did get them for coupling. Didn't do enough homework, evidently. But, on the bright side, they were only $7 total and can be replaced....uh....I mean.....WILL be replaced based upon the latest I have read. Thanks for the link. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted October 3, 2002 Share Posted October 3, 2002 Ed, If your amp only has one Pot per par of tubes for biasing then at the very least you need a matched set of tubes per channel. Not sure if your amp can have another set of Pots for biasing. Does it have a Selenium rectifier ? Is there Neg. voltage running to any of the pins of the Output tubes ? If there is neg voltage running to the output tubes installing the pots would be fairly easy if there is room for them. Let me know and if you want shoot me a email with a copy of the Schematic and I'll sort thru and see if the Mod MDeneen laided out for me will work on your amp. Craig Quote Link to comment Share on other sites More sharing options...
Clipped and Shorn Posted October 3, 2002 Share Posted October 3, 2002 Has anyone retrofitted their Fisher 500/800 with bias/balance controls? If you had modifications or upgrades done to this unit professionally can you say whether bias/balance controls were part of the mod/upgrade? Since these units utilize 7591 output tubes which are getter more scarce or impossible to find in NOS, it seems that the bias controls would be an asset when attempting to utilize an assortment of used 7591s. Anyone have any reports on the sonics of the Electro-Harmonix 7591A replacements used in these Fisher units? -c7s Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted October 4, 2002 Share Posted October 4, 2002 Hey Clipped.... I compliment you on your rolling avatar artwork and suddenly, it's Adam Sandler with beer gut and bad shorts standing next to someone that got up the nerve to ask them to stand there (is that pain on his face?) Heh... Or perhaps that is someone that LOOKS like Adam Sandler standing next to a loon with a bad T-shirt? REgardless, although I love abstract art, this is over the top! IS that you? What pier? kh Quote Link to comment Share on other sites More sharing options...
Gregorius Posted October 4, 2002 Share Posted October 4, 2002 I am currently using the EH 7591A's in my Fisher 800C. They are very smooth and detailed, not lacking at all. They sound good enough that I use them daily in my Fisher and the Westinghouse 7591A's that came with it are my spare set. They may not be NOS, but they are a very good tube and at $68 a matched quad from Paul @ BizzyBee, it's a no brainer. Regards, Greg Quote Link to comment Share on other sites More sharing options...
maxg Posted October 4, 2002 Share Posted October 4, 2002 Hey Kelly, Did I just miss the bargain of the century or are these junk??? http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=1384192258&rd=1 TIA Max Quote Link to comment Share on other sites More sharing options...
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