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EL34 Baby Huey Amplifier
EL34 Baby Huey Amplifier
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Old 14th March 2019, 07:37 AM   #381
tikiroo is offline tikiroo  New Zealand
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Join Date: Nov 2007
Location: New Plymouth
I haven't really experimented much with it. I bought a "DC 300W 20A CC CV" buck converter. I'm using a surplus 24V AC 50VA transformer rectified to 33V DC then dropping to 6.3V DC @ 4 amp load. Its a big voltage drop so efficiency not great, but heatsinks and inductor are barely warm. I bought the higher current module because I'm dubious about the advertised ratings.
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Old 14th March 2019, 02:40 PM   #382
Francois G is offline Francois G  United States
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Thanks for sharing you experience Mr. Tikiroo. This was very helpful. I believe the efficiecy of the conversion is >90%, so you are not loosing much energy in your conversion as evidenced by the cool heatsinks and inductor.

I shall do some experiments for my application in the near future, but your information will get me to my situation much faster.

Last edited by Francois G; 14th March 2019 at 02:51 PM.
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Old 14th March 2019, 04:43 PM   #383
Francois G is offline Francois G  United States
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"DC 300W 20A CC CV" buck converter

These devices seem to be really useful in enabling the using of cheap “odd voltage” tubes. My plan is to use 16gk6 tubes in stead of expensive 7189s.

Any experience to report.

Last edited by Francois G; 14th March 2019 at 04:45 PM.
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Old 14th March 2019, 05:27 PM   #384
Francois G is offline Francois G  United States
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Quote:
Originally Posted by Bfpca View Post
I have a regulated supply for hv set to 450v for el34. I am installing a switch so I can lower the HV for other tubes or plate currents I may want to try.
I am currently wiring up my chassis which is a big job with all the regulated supplies. I am getting there, may be done sometime next week. Just a hour or 2 now and then to work on it. I am looking forward to hearing it. When measuring distortion it seemed like the 2nd harmonic was dominant at lower levels, more so with the KT88 then the el34, perhaps because of the higher plate current I was running on the bigger tube.
Brian, how are things coming along?

I am very interested in you asessmemt of the Toirody transformers before I take the Plunge for output transformers. Any regrets. Like you I have a slew of suitable power transformers.

Last edited by Francois G; 14th March 2019 at 05:28 PM. Reason: Spelling error
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Old 20th March 2019, 05:36 AM   #385
Hanze Khronye is offline Hanze Khronye  Australia
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Join Date: Jan 2018
Thinking about AC heating the tubes and how some have experienced or expressed concerns about hum. I think very hard to accomplish this with a PCB and tight layout.

Seems to me that the traces could be cut at the sockets, to isolate the heater pins from the traces, and the heater circuit wired with twisted pair and floated at some distance from the PCB. Shielded or perhaps even not, I think AC heating is very possible with satisfactory results this way.

Can anyone confirm that the -ve supply which biases the output stage through the SS driver comes up before the main B supply?. Looks as though they would 'come up together' and a 30 second delay to the main B supply might be a welcome addition, would also give the heaters time to stabilize.

HK

Last edited by Hanze Khronye; 20th March 2019 at 05:43 AM.
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Old 20th March 2019, 08:46 AM   #386
Bfpca is offline Bfpca  Canada
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Join Date: Feb 2007
Location: Nova Scotia
EL34 Baby Huey Amplifier
Quote:
Originally Posted by Francois G View Post
Brian, how are things coming along?

I am very interested in you asessmemt of the Toirody transformers before I take the Plunge for output transformers. Any regrets. Like you I have a slew of suitable power transformers.
Hi Francois

The BH is nearly complete electrically but I still need to add some of the wood trim and a box to cover the voltage regulators which are on top of the chassis. I have some cherry and purple heart wood I wanted to use but a plan hasn’t gelled yet. I’ve been busy with lots of other stuff including a new pair of speakers that arrived yesterday.
From an objective point of view the Toroidy OT have excellent performance. The bandwidth is wide, going out to over 100khz and below 10hz as well as having low resistance windings for low loss. I have not listened to the BH yet but right as it sits now it should be operational for el34 use. I just have to wire a switch or 2 to allow for changing thee meter range for KT88 and to allow a couple of B+ options. Chassis was built from a scrapped industrial computer box. I’ll try to post some pics later. They need to be resized first.
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Old 20th March 2019, 08:52 AM   #387
huggygood is offline huggygood  France
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Join Date: Mar 2011
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Quote:
Originally Posted by tikiroo View Post
DC input is required. One pot ("CV") adjusts the output voltage, the other ("CC") adjusts output current. In practice you initially adjust the CC pot to the maximum current so it doesn't limit anything, then adjust the CV pot to get the voltage you want. Then with your normal expected load connected you can wind back the CC pot until the voltage just starts dropping (i.e. current limiting is overriding the voltage setpoint). Then wind the CC pot forward a turn or so. When turning on with cold heaters, the current will initially be limited and you get a slow rise in heater voltage. Once they are warmed up the voltage limit takes over.
thanks very much for your real good explanation
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