Sand diodes are new to me, so any recommendations on which brand and make of the sand diodes to get? Schottky, Wolfspeed, other? 1N4006, 1N4007, other?
It's guaranteed that on primary side the reflected load is -about- 20k.
If it omitted, the output is -even more- higher, as the tube "sees" much more impedance, and the loadline of tube not correctly defined.
p.s.
I don't like unloaded secondary. Some of transformers has bump at HF (at few ten kHz), If it loaded (R or series RC snubber), the bump is smoothable. Cons that output volume will decreasing.
If it omitted, the output is -even more- higher, as the tube "sees" much more impedance, and the loadline of tube not correctly defined.
p.s.
I don't like unloaded secondary. Some of transformers has bump at HF (at few ten kHz), If it loaded (R or series RC snubber), the bump is smoothable. Cons that output volume will decreasing.
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I have used a BH for the last 3 years with no unpleasantness. It's the rectifier in the power supply for a wee SE DHT Class A2 power amp (0.5W) using 1L5Gs and type 52s. Cold-cathode (or gas discharge) rectifiers are closely related to gas discharge voltage regulators (like the 0D2 etc). The 0Z4A was made and used well into the 1960s.
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Looking at that data sheet for the L413, my German is lousy but is that some advice at the bottom to use some sort of current limiter for the 150mA for the DC filament? (Gleichstrom-serienröhre)
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What voltage are you using with the BH? The specs say 350V minimum starting voltage. What are you using? My design calls for only 165Vac and dc rectified, therefore I believe the BH won't be suitable.
I use a 350-0-350 VAC power transformer to supply the BH. I followed the manufacturer's recommendations and placed 0.1uF capacitors across each secondary and a 4.7uF capacitor as the first filter, followed by a choke (the data sheets are from John Atkinson's very helpful One Electron archive at: https://www.one-electron.com/Archives.html). Thereafter I used C-R-C filtering to further reduce ripple and set the required voltages (in my case 210V and 165V).
While 165V is achievable, your proposed circuit draws about 30mA, which may be on the low side for good operation of the BH. Though Raytheon didn't suggest a minimum operating current for the BH, it recommended at least 200mA for the BH's bigger sibling, the 350mA rated BA. So I guesstimated that a BH might need to pass at least 75mA to operate well (I don't know for sure - I didn't try lower current operation).
In the circumstances, your choice of silicon diode rectifiers seems sensible. Load current aside, the BH is not an efficient device, especially when compared to silicon diodes - there is a considerable drop in voltage across the BH rectifier which increases somewhat as the load current increases.
In fact my selection of the BH was NOT sensible engineering but a desire to build an amp in which all the valves were at least 80 years old. The BH I am using is 98 years old and the type 52s have just turned 90. The 1L5Gs are spring chickens at a spritely 88 years of age. I call the amp The Octogenarian.
While 165V is achievable, your proposed circuit draws about 30mA, which may be on the low side for good operation of the BH. Though Raytheon didn't suggest a minimum operating current for the BH, it recommended at least 200mA for the BH's bigger sibling, the 350mA rated BA. So I guesstimated that a BH might need to pass at least 75mA to operate well (I don't know for sure - I didn't try lower current operation).
In the circumstances, your choice of silicon diode rectifiers seems sensible. Load current aside, the BH is not an efficient device, especially when compared to silicon diodes - there is a considerable drop in voltage across the BH rectifier which increases somewhat as the load current increases.
In fact my selection of the BH was NOT sensible engineering but a desire to build an amp in which all the valves were at least 80 years old. The BH I am using is 98 years old and the type 52s have just turned 90. The 1L5Gs are spring chickens at a spritely 88 years of age. I call the amp The Octogenarian.
Hi everyone, hope all is well. Some time has passed and I finally have the pre-amp up and running. The current schematic is attached. I need some help on 2 questions.
1. When the pre-amp is turned on, there is a loud "pop" which is originating from the OZ4 cold cathode rectifier. Wondering if you see anything wrong with the schematic or ideas to remediate this?
2. The Line Out transformer secondary is 600ohms. I have not put a resistor across the secondary, as the 600ohm load is OK with the 10K input load on the solid state power amplifier. Do you believe I should add a resistor across the secondary?
Otherwise, the unit is working well.
Thanks
1. When the pre-amp is turned on, there is a loud "pop" which is originating from the OZ4 cold cathode rectifier. Wondering if you see anything wrong with the schematic or ideas to remediate this?
2. The Line Out transformer secondary is 600ohms. I have not put a resistor across the secondary, as the 600ohm load is OK with the 10K input load on the solid state power amplifier. Do you believe I should add a resistor across the secondary?
Otherwise, the unit is working well.
Thanks
The schematic definitely wrong.
The 4V filament battery must to connect to filament pins and 9V battery working as bias supply (from one filament point to ground).
Is filament always heated?
If not, try to turn on filament heating (when tube conducts current) and power supply turn on at different times.
p.s.
If input voltage controller switch isn't "make before break" type, must to use -for example 100k- grid leak resistor (from grid to ground).
The 4V filament battery must to connect to filament pins and 9V battery working as bias supply (from one filament point to ground).
Is filament always heated?
If not, try to turn on filament heating (when tube conducts current) and power supply turn on at different times.
p.s.
If input voltage controller switch isn't "make before break" type, must to use -for example 100k- grid leak resistor (from grid to ground).
Bela, thanks for the response. Good catch on the filaments. Here is the updated schematic and I also inserted the grid leak resistor.
Meanwhile, any thoughts on the loud "pop" when the amp is turned-on?
Meanwhile, any thoughts on the loud "pop" when the amp is turned-on?
Try to separate the PSU for the amp.
If both channel use the same PSU, try to detach its, and load PSU with 4k7 15-25W resistor (the dissipation will be about 5W).
Try to measure voltage on C2 (30uF), C3 (250uF) and on the output.
If "pop" can be heard even so, probably the cold rectifier "jerking" the PT with too much current at startup.
If both channel use the same PSU, try to detach its, and load PSU with 4k7 15-25W resistor (the dissipation will be about 5W).
Try to measure voltage on C2 (30uF), C3 (250uF) and on the output.
If "pop" can be heard even so, probably the cold rectifier "jerking" the PT with too much current at startup.
So, I put in a varistor and that did not help the "pop". Also, the grid leak resistor helped with the occassional "make before break" issue, which is nice.
I am going to look into alternative rectifiers. Trying to avoid another darn transformer for a rectifier filament.
I am going to look into alternative rectifiers. Trying to avoid another darn transformer for a rectifier filament.
Try to put 22R...220R resistor (value depends on the C3 voltage and Od3 voltage difference) amongst rectifier and C1.
Try a different 83 make, or an earlier year of production. The newer ones do indeed sound a little unpleasant. On average, a lot better sound than the 866 imho.
FlaCharlie - this is a pre-amp. I am using Finemet 10K:620 nanocrystalline line-out transformers.
Finement Line Out Transformer
Finement Line Out Transformer
Yikes! $485 each? Hope they work well. I’ll stick to using caps.
You’re definitely using some interesting oddball tubes. I'm semi-familiar with the rectifiers and I’ve used a 0D3 or one of its siblings but I’ve never heard of the L413, B405, B406. Are those early European tubes?