Digital Man Posted July 5 Author Share Posted July 5 3 minutes ago, VanArn said: Yes, get your technician to test the mains transformer to find out what voltage is present on the HT windings. Was the HMV radiogram an earlier mono type as 6V6GT valve suggests such a scenario. Yes, it was mono in a SE configuration, made in either ‘58-‘59 Link to comment Share on other sites More sharing options...
Digital Man Posted July 6 Author Share Posted July 6 Hi, I have been going through my messages with the builder, of that power amp of mine that we are discussing here, he had wired it up, with the choke from the same chassis as the power transformer, to some EL34's in PP, he said it worked fine, delivering around 50 watts for the pair. I may have also, phrased the specs wrongly previously as well, so just in case, here are his phrasing of those specs, ( by the way, it was not Earle who gave me this set of specs, he gave me some other specs for it, which I cannot locate for now ) so, the specs as originally conveyed to me are 240 vAC supplies 5 vAC for the rectifier heater 6.3 vAC for the remaining heaters of octal 9 pin or 7 pin bases 400 v rectified and filtered DC for the HT supplies He also says that it can run with these valves 6L6 - 6CA7/EL34 - 6BQ5 - 6AQ5 - 6M5 - 6GW8 and a 6DQ6B Link to comment Share on other sites More sharing options...
aussievintage Posted July 6 Share Posted July 6 2 hours ago, Digital Man said: 400 v rectified and filtered DC for the HT supplies yeah that's a bit different. Still too high for 6V6's as is. I'd be really careful about some of the other suggestions too. Some designers like to push limts. Link to comment Share on other sites More sharing options...
Digital Man Posted July 6 Author Share Posted July 6 1 hour ago, aussievintage said: yeah that's a bit different. Still too high for 6V6's as is. I'd be really careful about some of the other suggestions too. Some designers like to push limts. To which suggestions are you referring to ? Link to comment Share on other sites More sharing options...
aussievintage Posted July 6 Share Posted July 6 (edited) 10 hours ago, Digital Man said: To which suggestions are you referring to ? Well, 6AQ5 is only rated to 275 volts !! 6L6 is maxed at 375. I would not put 400 on it. 6BQ5 is 550 (without any plate current) and 300 after that. 6M5 is same rating as 6BQ5 Now it also depends on how that 400VDC is measured. Will it sag under load? How much drop through the output transformer and cathode resistor? ... but you get the idea. Why push a valve to it's maximum ratings or over? You won't, in reality, really notice the extra power. Edited July 6 by aussievintage Link to comment Share on other sites More sharing options...
aussievintage Posted July 6 Share Posted July 6 btw. El34 is still your best choice as it is a commonly used valve still. Some of the others will be hard to buy new. However, watch the heater current as the EL34 draws twice as much as many others. You said he had it running with two in push-pull. How hot did the transformer get over an extended period, because it will get even hotter running EL34's single ended? I had a transformer from equipment that ran two 6CM5's in PP, that cooked trying to cope with two EL34 in SE. Link to comment Share on other sites More sharing options...
Digital Man Posted July 6 Author Share Posted July 6 That’s my concern too, what about using KT66, KT77 or KT88 ? Also, I am open to going to PP, but would rather go SE/SET, and if the 400 v is too high and it was being originally used with 6v6 gt, then which valve would it suit better ? Link to comment Share on other sites More sharing options...
aussievintage Posted July 6 Share Posted July 6 1 hour ago, Digital Man said: That’s my concern too, what about using KT66, KT77 or KT88 ? Also, I am open to going to PP, but would rather go SE/SET, and if the 400 v is too high and it was being originally used with 6v6 gt, then which valve would it suit better ? I am not convinced the original set put 400V on the plates of the 6V6's but I haven't opened up many old hifi designs that used them, just guitar amps. That said, the 6V6 sounds great as a SET hifi amp - I have one I built that can handle most octal valves and have tried them a few times. The KTxx valves handle the higher voltages, but their heater currents are also higher, like the EL34. Maybe as great as three times as much heater current as a 6V6, so I worry about the power transformer handling it. That resource I gave you a link to, will enable you to look up all these things and compare. Maybe use it with 6V6s, and if they arc over, then try dropping the HT with a power resistor (crude but it can be done). Link to comment Share on other sites More sharing options...
Digital Man Posted July 9 Author Share Posted July 9 On 21/11/2020 at 9:39 AM, aussievintage said: Having built many different SE and SET amps from leftover parts from old equipment like this, let me just say you can achieve a very fine sounding amp. The 6V6 can sound great in triode mode, and I am sure you could get a couple of watts from it, depending on voltage and loading etc. That makes it roughly on the same level as the 2A3 DHT style amps many people like, and that I am currently using. My speakers are 95db efficient and I get told to turn it down Also, with a 6V6 octal socket, you can also plug in 6L6, 6550, and all sorts of valves in that family. They will run at 6V6 bias conditions aprox. but will sound subtly different, and allow you to experiment. My tech guy said the very same thing, about running different octal based valves in place of the 6v6 Link to comment Share on other sites More sharing options...
aussievintage Posted July 9 Share Posted July 9 16 hours ago, Digital Man said: My tech guy said the very same thing, about running different octal based valves in place of the 6v6 Actually with the addition of two alternative power resistors in the cathode bias, and adding a jumper to select them, that same amp became able to run EL34, 6V6 6L6 6550 etc etc at difference bias points. I know the load impedances were not ideal, but in triode mode, that is less troublesome. Link to comment Share on other sites More sharing options...
Digital Man Posted July 22 Author Share Posted July 22 (edited) Hi all, Just a quick update, I bought the Rola Output Transformers, OPT1, specs are 10 watts, Primary 7K and Secondary 8 Ohm, here are some pictures of them, all I need now is some covers for them, if anyone knows what type of covers, please let me know Edited July 22 by Digital Man Link to comment Share on other sites More sharing options...
Digital Man Posted July 22 Author Share Posted July 22 I may as well show you all the chassis and transformers as well Link to comment Share on other sites More sharing options...
RoHo Posted July 23 Share Posted July 23 On 22/7/2024 at 7:44 PM, Digital Man said: Hi all, Just a quick update, I bought the Rola Output Transformers, OPT1, specs are 10 watts, Primary 7K and Secondary 8 Ohm, here are some pictures of them, all I need now is some covers for them, if anyone knows what type of covers, please let me know This place has big selection http://www.mableaudio.com/en/products.asp?sid=83 Link to comment Share on other sites More sharing options...
Digital Man Posted July 23 Author Share Posted July 23 Thanks, I will check them out Link to comment Share on other sites More sharing options...
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