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SE807 Triode Dick Amplifier Questions
SE807 Triode Dick Amplifier Questions
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Old 11th April 2017, 01:36 AM   #11
Mickeystan is offline Mickeystan  United States
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SE807 Triode Dick Amplifier Questions
lilstripe,

The 5 volt winding would connect to pins 2 and 8 of a 5U4 rectifier tube (assuming you go with this tube), and then the connection to the standby switch would connect to either pin 2 or 8, your choice it does not matter. You do this as the rectifier filament winding with this transformer does not have a center tap, which is OK. The one 6.3 volt filament winding will serve all tubes for both channels assuming you build two channels to make a stereo implementation. When doing this you will not ground the center tap of the 6.3 volt winding. Rather you will need to connect it to junction of the 390k, 82k and 100uf capacitor (components that used to connect to the center tap of the 6SN7 srpp heaters). The opposite end of the 390k will connect to the place it currently connects to. These two resistors and the bypass capacitor (100uf cap) serve to elevate the heaters to about +75 volts. Having all heaters elevated will not be a problem. Elevating the heaters will help to further reduce any heater induced hum that may come in near the front end of the amplifier. Hope this helps.

Mickeystan

Last edited by Mickeystan; 11th April 2017 at 01:39 AM.
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Old 11th April 2017, 06:17 AM   #12
Miles Prower is offline Miles Prower  United States
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Quote:
Originally Posted by lilstripe View Post
Long time lurker, first time poster...

I have some questions about the Triode Dick Single Ended 807 Amplifier design.
It would be helpful if someone could help answer my questions and if they have the time, describe how they derived the answers. I'm trying to learn.
I've built a lot of SS electronics gear but new to building tube amps. I get the basics of electronics but am no expert per say.
The first thing you need to consider is that hollow state uses DC rail voltages much higher than most solid state. Do be careful.

Questions as circled in the attached picture:
Quote:
1. Is the purpose of this switch to allow the filaments to light up and then turn this switch on to apply the B+?
This is a real bad idea. Hollow state diodes don't like hot switching and may protest by arcing over. Even if that doesn't happen, they won't last long. Secondly, open that switch and you're 450V above DC ground. That's a nasty shock hazard.


Quote:
2. What current rating and/or DCR should I seek for the 10H chokes?
The DCR of any decent ripple filter choke should be irrelevant when compared to the total load resistance. Since this is a SE design, the plate current should be ~50mA. That would be the current rating. You have to remember that the definition of inductance:

L= (N * phi)/I

only applies to air coils where the relationship between magnetic flux and current is linear. Ferromagnetics make for a non-linear relationship, but the concept is just so useful that inconvenience is ignored. The current "rating" of the choke has nothing to do with the max current capability of the wire, but rather the current needed to produce the nameplate inductance.

Try measuring the inductance with an RLC bridge, and you're likely to see an inductance of hundreds of henries. Try plugging it into a wall socket while measuring the current, and you're likely to calculate an inductance of a few hundred millihenries.

In the first case, your RLC bridge was using a sense voltage of 1.0VP. Plugging it into a wall socket is likely to saturate the core which greatly reduces the inductance (see above formula and ask what happens if phi can't increase, but current can.)

Quote:
3. Power rating and/or PA rating of the OPT if 5K secondary is selected?
4. Any recommendations for an easy to obtain transformer that meet these specs for someone in the USA? Could always add separate filament transformers under the chassis if needed.
10 - 15W should be good to go. No need for overkill. Try Edcor
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Old 11th April 2017, 09:26 AM   #13
lilstripe is offline lilstripe  United States
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Now I'm really confused.
I'm hearing 150-200ma for the choke from one person and 50ma from another.
Help...
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Old 11th April 2017, 09:34 AM   #14
jazbo8 is offline jazbo8
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SE807 Triode Dick Amplifier Questions
That's 50mA per channel, also see post #8.
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Old 11th April 2017, 10:54 AM   #15
lilstripe is offline lilstripe  United States
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Correct, but it also has two chokes in the design, one per channel. So if its 50ma, I should be safe using a 75 or 100ma choke?

Thanks
lilstripe
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Old 11th April 2017, 11:01 AM   #16
jazbo8 is offline jazbo8
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SE807 Triode Dick Amplifier Questions
Of course, even 75mA will be more than enough.
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Old 11th April 2017, 12:38 PM   #17
Ketje is offline Ketje  Belgium
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Like this i think
Mona
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File Type: jpg TD-807se.jpg (58.2 KB, 307 views)
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Old 11th April 2017, 04:44 PM   #18
lilstripe is offline lilstripe  United States
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Thanks for putting that into a picture!
Others agree?
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Old 11th April 2017, 05:57 PM   #19
Mickeystan is offline Mickeystan  United States
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SE807 Triode Dick Amplifier Questions
lilstripe,

Ketje (Mona) has the schematic illustrated correctly. In response to my original choke recommendation of 150ma, others have commented that you can do OK with a 50 ma chokes. In my opinion you pushing the minimum limit at 50ma. I originally stated what I did as the Power transformer is rated for 300 milliamps of output current on the original schematic. Please understand that the power transformer has way more current capability than this amplifier needs. Thus it is over kill from the high voltage winding capability. Since this Class A amplifier will draw approx. 50 milliamps if built only a single channel mono or approx. 100 ma if built stereo you can save money on the power transformer as well if you want to built it as needed vs over designed as was originally done by Triode Dick. If you choose to built it with a more appropriate power transformer, I would direct you to use the Allied Electronics transformer part number 70008996 which is their model 6K7VG. This transformer has same set up for the filaments but is built with a 375-0375 volt secondary rated at 150 millamps. Thus, if you want to built this amplifier with this option, the power transformer is available and for sale at Allied Electronics for $52.86. Hope all of this is not leading to further confusion for you. Best of luck on you upcoming build!

Mickeystan
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Old 12th April 2017, 02:16 PM   #20
lilstripe is offline lilstripe  United States
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Question - Transformer Related

Hoping to build this design with a laydown style mount transformer (old dynaco st70 style look). I found a decent one commonly available from ClassicTone but the specs are slightly less on the B+. The 6v and 5v are the same.
It would be 710v @ 200ma vs the original design of 760v @ 300ma (which the 300ma looks overkill based on all your previous comments). Would the 710v work or what would be the implications?

How would that play out in this circuit?
Thanks
Lilstripe
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