Or just use a regular transformer and add external series resistance to taste.
Copper losses should be pretty straight line linear, so a resistor should provide a very close result.
Search found 2704 matches
- Thu Oct 26, 2023 8:02 pm
- Forum: Technical Discussion
- Topic: Power transformer fails
- Replies: 63
- Views: 55657
- Tue Oct 24, 2023 10:55 pm
- Forum: Vox/Hiwatt Discussion
- Topic: Smoothing caps?
- Replies: 7
- Views: 45627
Re: Smoothing caps?
Electrolytic caps are wide tolerance type components.
In the old days, the tolerance for higher voltage types was as loose as +100% to -50%.
These days +/-20% is typical
Hence for these purposes, 220 = 250.
In the old days, the tolerance for higher voltage types was as loose as +100% to -50%.
These days +/-20% is typical
Hence for these purposes, 220 = 250.
- Sun Oct 22, 2023 8:36 am
- Forum: Technical Discussion
- Topic: Modifying a bias circuit to work with no PT center tap
- Replies: 18
- Views: 11187
Re: Modifying a bias circuit to work with no PT center tap
The RC high pass filter component values before the bias rectifier largely determine the rectified V DC at the bias reservoir cap.
Such that if more voltage is required, the R or the C or both values could be increased.
- Fri Oct 20, 2023 9:10 am
- Forum: Technical Discussion
- Topic: Out Of Curiosity...
- Replies: 11
- Views: 4227
Re: Out Of Curiosity...
The builder of my guitar amp said "The bias pot is on the left hand side of the board. the beige square with black dial. Set it for 25mV across the 1Ω resistors on each power tube cathode." … so I'm not truly in affect changing any hot or cool biasing on the power tubes... right? No, not right. Fro...
- Fri Oct 20, 2023 8:56 am
- Forum: Technical Discussion
- Topic: Power transformer fails
- Replies: 63
- Views: 55657
Re: Power transformer fails
… I have changed about everythin partwise, filtercaps, rectifiers etc. Only visible sign in the amp iyself was a burnt grid resistor. For a 6L6 to cause a 470R 5W screen grid resistor to become damaged, the valve in the socket must either have shorted badly, or have lost bias. HT fuses are a really...
- Thu Oct 19, 2023 7:44 pm
- Forum: Technical Discussion
- Topic: shielding with plate voltage
- Replies: 19
- Views: 4652
Re: shielding with plate voltage
As the input stage anode is fed via 100k, the voltage / current at the input if the screened cable shorted is rather limited.
- Thu Oct 19, 2023 10:51 am
- Forum: Marshall Discussion
- Topic: Primary impedance of original jtm 45 ot?
- Replies: 18
- Views: 6288
Re: Primary impedance of original jtm 45 ot?
Have you checked the high frequency to ultrasonic frequency and phase response of your’s? Mine has a weird resonant peak and phase shift around 40kHz. I didn't I don't have balanced signal generator, maybe runing the secondary with SG and solid state amp will work, but never tried. I think the only...
- Wed Oct 18, 2023 4:56 pm
- Forum: Technical Discussion
- Topic: Do I really need a tube rectifier? Lazy amp tech's journey
- Replies: 12
- Views: 2271
Re: Do I really need a tube rectifier? Lazy amp tech's journey
The issue with a valve rectifier and the standby switch depends on whether it’s a hot switching arrangement, ie the switch, when open, it interrupts the reservoir cap’s charging current. If it does then it’s hot switching and will probably result in the peak anode current limit of ghe rectifier bein...
- Wed Oct 18, 2023 10:34 am
- Forum: Technical Discussion
- Topic: Do I really need a tube rectifier? Lazy amp tech's journey
- Replies: 12
- Views: 2271
Re: Do I really need a tube rectifier? Lazy amp tech's journey
... Too tired of replacing bad rectos! At least when they fail they make a cool light show. 8) That’s nuts, it’s the simplest thing to eliminate that failure mode. Just re-arrange hot switching standby switches (or just leave them permanently closed), most importantly fit back up silicon diodes and...
- Mon Oct 16, 2023 11:16 pm
- Forum: Technical Discussion
- Topic: Do I really need a tube rectifier? Lazy amp tech's journey
- Replies: 12
- Views: 2271
Re: Do I really need a tube rectifier? Lazy amp tech's journey
The slow ramp up of HT voltage, the elimination of HT surge voltage / current, provided by a GZ34 is a wondrous thing. Obviously some people don’t appreciate it, or at least don’t think it’s worth the additional infrastructure etc required to support it. That’s fine, suitable solid state diodes are ...
- Sun Oct 15, 2023 11:37 pm
- Forum: Marshall Discussion
- Topic: One cathode follower, 2 tone stacks
- Replies: 10
- Views: 3423
Re: One cathode follower, 2 tone stacks
Adding a 2nd tonestack to the DCCF has an obvious, significant effect on its large signal waveform.
The difference may not be particularly audible though, it’s apparent but certainly it doesn’t change the tonal character.
I decided not to follow that option though.
The difference may not be particularly audible though, it’s apparent but certainly it doesn’t change the tonal character.
I decided not to follow that option though.
- Sat Oct 14, 2023 12:57 am
- Forum: Marshall Discussion
- Topic: Primary impedance of original jtm 45 ot?
- Replies: 18
- Views: 6288
- Sat Oct 14, 2023 12:49 am
- Forum: Marshall Discussion
- Topic: Primary impedance of original jtm 45 ot?
- Replies: 18
- Views: 6288
Re: Primary impedance of original jtm 45 ot?
The first year or 2’s production mostly used the RSDeluxe, hard wired for 6k6 primary and 15 ohm secondary. https://i.ibb.co/pPwMwm5/66-RSOT-4.jpg https://i.ibb.co/xFLykLV/RS-Page-1.gif https://i.ibb.co/59PP9vH/RS-Page-2.gif Subsequently the Drake 784-103 was mostly used, 8k primary to 8, 16 & 100V ...
- Wed Oct 04, 2023 9:23 pm
- Forum: Technical Discussion
- Topic: Primary impedance for OTs - output and tone
- Replies: 16
- Views: 5181
Re: Primary impedance for OTs - output and tone
Me either!
I was just working on the basis of low order harmonics predominating and it being push pull, so there should be a fair degree of cancellation of even harmonics
- Wed Oct 04, 2023 9:18 pm
- Forum: Technical Discussion
- Topic: Primary impedance for OTs - output and tone
- Replies: 16
- Views: 5181
Re: Primary impedance for OTs - output and tone
All of the OTs mentioned are kinda lofi, low spec type. Perhaps not quite as low spec as those in equivalent Gibson models of the same era.