Cathode bias bassman.
In the process of planning a Bassman build.
Cathode bias bassman. I would like to use the iron I have from a Baldwin organ that ran a 5U4GB, 2-6L6 and a bunch of 12AX7/12AU7's The transformer has the following taps: 372V HT Red pair with CT 13. Hoffman Amplifiers Tube Amp Forum, Biasing- do newer re-issue Fender Bassman' have bias pots? During 1952, the Fender 5B6 Bassman amplifier was introduced as a combo amplifier cabinet that included the amplifier chassis combined with one 15" speaker. Dec 18, 2020 · Converting the Bassman circuit to cathode bias will change the feel and power output of the amp. For cathode bias you would simply place a resistor (with a small bypass cap across it) between pin 8 and ground. The 25/50 cap is the bias filtering cap, and yes, it should be uprated - 63V min, I use 100V. I am not planning on changing any values in the amp yet, as far as resistance goes The design is fully derivative of Fender stuff with some tone stack component value changes. I voiced Mar 29, 2009 · 25uF 50V is sort of a standard value for Fender in conjunction with the 250 Ohm bias resistor. I noticed that all but the 5B6 versions have what appears to be a 48V biasing circuit. Of course it might be a moot point, since the 5F6 Bassman didn't have adjustable bias anyway. Am I in the Ball Park? Do I need to drop the screen Apr 4, 2015 · If you do plan to use the amp as a tester then try to match V1's 100k load resistors and 1. Without them you need to use some other method to measure the idle current of the tubes such as shunting the OT with a DMM. Its DC-coupled cathode follower and tone stack sit prominently in the signal path of the Soldano SLO, Traynor YBA-1, and Vox AC30 (without a middle control). There are a few bias meters on the market that use this method, including the SwAMProbe (it doesn't measure across a resistor, rather, it breaks the cathode circuit so you can insert a milliammeter for direct cathode current measurement), and the Bias King. 6V6 have more of a honey sweet tone and put out less wattage In the process of planning a Bassman build. Jul 30, 2021 · Author Topic: Bassman AB165 bias adjustment (Read 3174 times) 0 Members and 1 Guest are viewing this topic. 7V Yellow pair I do not have a 48V tap. Bias current is the amount of electrons flowing from the cathode to the plate with no audio signal on the control grid (idle current). Notice the bias balance was added, but the bottom of one of the 100k bias feed resistors shows -45v where the AA864 showed -44v at a similar point in the circuit. The Bassman's gamma-network front end is the hands-down favorite of builders to this day. Note: cathode is (I think the term is elevated) by tying it to my artificial center tap on my heater circuit. How to Measure Bias This webpage offers two ways to calculate tube bias and plate dissipation. 5V across the 10W resistor. The 1952–1954 [1] 5B6 Bassman amplifiers had two 6SC7 or 6SL7GT pre-amp tubes, two 5881 power tubes and a single 5U4G rectifier tube. What are my Fixed and Cathode bias? If so, anyone have spec/layout for such a thing? wb 2006-07-29 02:27:41 UTC Post by guitarPsych Would it be easy to mod an AB165 Fender Bassman to have a switch between Feb 8, 2018 · The bias difference is not important as the amp will be adjustable fixed bias anyway. However they do make biasing the amp both easier and safer. Mo' like BF for Blackface, fixed bias etc. For amps with cathode bias resistors you can simply measure their voltage drop and use the Tube Dissipation Using Cathode Resistor Voltage Drop calculator. In stead of grounding the 6L6 cathodes, insert a parallel-coupled 250 ohm/ 5w resistor and 25µF/50V cap between ground and the two cathodes. The 6G3 Deluxe and Princeton Reverb both run fixed bias and bias vary tremolo. 5k cathode resistors so you can take bias readings of the two halves of the tube to check for balance. Aug 18, 2023 · Using cathode bias causes the individual tubes to "pull toward an average" and exhibit less variation in measured characteristics. The terms cathode bias and fixed bias are often used to describe amps but lots of folks are not really sure what they mean. Hoffman Amplifiers Tube Amp Forum, Biasing- do newer re-issue Fender Bassman' have bias pots? Dec 18, 2020 · Converting the Bassman circuit to cathode bias will change the feel and power output of the amp. Sep 8, 2006 · Can a Bassman Reissue be cathode biased? I know that in stock form, they are fixed bias. The on-line Weber calculator gave me 20W @ 57ma plate dissipation when I plugged in these numbers. Perhaps the mixed-bias method was used to combat the tube-variation problem PRR described. I will briefly provide a technical explanation and then provide some bullet points of the major differences in tone, maintenance and power. AB165 bassman style pre-amp but without the caps across the plate resistors, 6G11 power section but with cathode bias and the presence control like the 6G6 bassman. Using higher capacitance modifies the circuit time constants, leading to a stiffer but slower bias supply. Nov 23, 2022 · OK. Working on an mostly original ab165 bassman, vintage 1966. I finally got the amp to working after redoing part of my cap job on the third/shared cathode circuit ground. i suspect the LTD is closer to the original 5F6 schematic. It will also overdrive a bit easier which may be a good thing if that's what your after. Bias shift tremolo isn't exclusive to cathode bias. If this can be done, what effects/benefits will it A 490ohm cathode resistor with a 28uf@50V cap yielded 29. If this can be done, what effects/benefits will it The 5F6A Bassman circuit shown above has fixed bias and does have a bias filter cap at its output (lower 8uF Bias Filter cap) so the MV AC Ground cap is not needed. So I want to tackle that. Feb 5, 2025 · I have a mid 60s Bassman style amp and cascaded the V1 Gain stage into unused triode of V2, I had some issues with oscillation but cured with some snubbing caps: See full list on robrobinette. 5V Brown pair 5. A little cathode bias can pull disparate tubes together, and the bias-balance handles the rest. " You measure the output transformer's voltage drop and Jan 14, 2013 · Biasing a 59 Bassman Ltd by analogopher » Mon Jan 14, 2013 9:46 pm What is Bias? Bias voltage is the voltage difference between a tube's cathode and control grid. Amp does have some resistor noise. I used the smaller transformer from the early models (Mercury Magnetics equivalent) to keep B+ in the lower range for the 5881's. Adding the 150Ω resistors would increase the bias, and the AC568 would idle cooler as the new cathode bias adds to the essentially-same fixed bias. The tube can stop the flow completely (called cutoff) or let it flow at maximum (called Mar 27, 2024 · Apparently Fender has made both a '59 Bassman reissue and a '59 Bassman LTD. 6V Green pair 6. It was designed to generate 26 watts at an 8-ohm impedance load, and offered a cathode-based bias The grid bias supply in particular is fixed and taken from the same transformer tap as the Bassman. Feb 8, 2018 · The bias difference is not important as the amp will be adjustable fixed bias anyway. The output transformer has been re-tooled to run a pair of 6V6 output tubes with cathode bias (rather than the original 5881 in grid bias) and the interleaving matches the original seven section buildup, contributing to its open top end, coupling efficiency, and airy response. My recommended bias measurement method is the " Output Transformer Resistance Method. . The only caps I replaced are the filter caps, cathode caps, and bias cap. An amplifier tube controls the flow of electrons running through it. Feb 5, 2025 · Re: Bassman ?AB165 - cathode bias/ high pitch noise etc « Reply #4 on: February 05, 2025, 03:10:09 pm » for test, just "open" the circuit, so no NFB then check for your high-pitched noise Logged The 5F6A Bassman circuit shown above has fixed bias and does have a bias filter cap at its output (lower 8uF Bias Filter cap) so the MV AC Ground cap is not needed. com We think that the cathode bias circuit design of the 5e3 works very well in the Bassman. The JMP50 Model 1987, however, shifts the grid supply to one phase of the high-voltage secondary, eliminating the need for a lower-voltage tap, and adds a variable resistor to enable the bias voltage to be adjusted. I will be getting me 59 BMRI retubed soon, and had planned on getting a bias trim pot installed, but then I wondered if it could be cathode biased. l28189vymm4vu4wwmxomsnlmerovutzwi3k2p8jzvxpxi