Search found 758 matches

by jjman
Thu Jun 23, 2016 11:50 pm
Forum: Technical Discussion
Topic: Phase Inverter Distortion
Replies: 5
Views: 1445

Re: Phase Inverter Distortion

It is increasing the "load." Similar to increasing the load in a truck. Poorer acceleration and deceleration.
by jjman
Wed May 11, 2016 12:25 am
Forum: Technical Discussion
Topic: Grid Resistor Value Determinations
Replies: 11
Views: 3924

Re: I'll look at the information you posted

............Another question- If there is no substantial current flowing in the bias circuit, how do different value bias feed resistors affect the bias on the output tubes? ..............silverfox. The flow of current in the bias circuit does not flow thru the grid / bias feed resistors. The bias ...
by jjman
Wed May 04, 2016 11:06 pm
Forum: Technical Discussion
Topic: Preamp bias-vary tremolo schematic/layout
Replies: 2
Views: 736

Re: Preamp bias-vary tremolo schematic/layout

http://el34world.com/charts/Schematics/files/airline-wards/Airline-Wardss_gvc-9058a.pdf http://el34world.com/charts/Schematics/files/harmony/harmony_h410.pdf http://el34world.com/charts/Schematics/files/kalamazoo/kalamazoo_m2s.pdf http://el34world.com/charts/Schematics/files/gibson/Gibson_skylarkga5...
by jjman
Sun Apr 24, 2016 2:23 am
Forum: Technical Discussion
Topic: Danelectro 6sj7 Vibrato
Replies: 6
Views: 1390

Re: Danelectro 6sj7 Vibrato

Should be about 8ma thru that resistor at idle. Screens would draw more at louder outputs since class AB.

2200=v/.008

.008x2200=v

v=17.6

w=va
w=17.6x.008
w=0.14

No way that resistor needs to be that big. I like a ~3watter early is a PS that small.
by jjman
Thu Apr 14, 2016 12:30 am
Forum: Fender Discussion
Topic: Princeton Reverb vs Deluxe Reverb clean output volume
Replies: 10
Views: 2797

Re: Princeton Reverb vs Deluxe Reverb clean output volume

Has it been documented that a stock PR clips in the PI or preamp before the 6v6s? I know my DR clips in the 6v6s 1st so cleaning up or increasing voltages in its preamp or PI isn't going to provide more clean output from the speakers. I know the PR has a cathodine PI which does not provide signal bo...
by jjman
Wed Mar 23, 2016 8:41 pm
Forum: Trainwreck Discussion
Topic: CTS pots New vs Vintage
Replies: 10
Views: 2308

Re: CTS pots New vs Vintage

30% seems way to close to liner to work in a volume application to me. The graphs I've seen all show ~10% for non linear and non-reverse types.
by jjman
Fri Feb 19, 2016 12:50 am
Forum: Technical Discussion
Topic: Touch-Sensitivity: Myth or Reality?
Replies: 24
Views: 3274

Re: Touch-Sensitivity: Myth or Reality?

Check out Dave Edmunds' "Baby Let's Play House." Especially the last 5 seconds. No better example in a song that I know of.

https://www.youtube.com/watch?v=5NHjEW01DsM
by jjman
Wed Feb 10, 2016 12:24 am
Forum: Technical Discussion
Topic: Measuring Screen Grid Dissipation
Replies: 35
Views: 4523

Re: Measuring Screen Grid Dissipation

Using DC measurements under signal may or may not be numerically accurate depending on the meter. But the increasing reading is in the right direction since this is most likely class AB. A scope is needed to see for sure.
by jjman
Sat Feb 06, 2016 9:12 pm
Forum: Technical Discussion
Topic: SE EL34 Plexi-verb
Replies: 137
Views: 12125

Re: SE EL34 Plexi-verb

The input to the Belton is grounded in the scheme. Not sure if that was pointed out. It should probably go only to the wiper of the pot.
by jjman
Tue Jan 12, 2016 12:29 am
Forum: Fender Discussion
Topic: 79 Deluxe Reverb volume problem
Replies: 9
Views: 2447

Re: 79 Deluxe Reverb volume problem

Make sure the path to ground is good. I think this means its physical mount to the chassis in this case.
by jjman
Sat Dec 19, 2015 3:16 am
Forum: Technical Discussion
Topic: Adjustable cathiodbiae
Replies: 5
Views: 1008

Re: Adjustable cathiodbiae

I use 2 470ohm resistors + 2 100ohm pots on a pair of 6v6s to do this. Pots are 5wt wire wound. Each has its own bypass cap.
by jjman
Sat Dec 12, 2015 6:28 pm
Forum: Technical Discussion
Topic: How do you tell a customer...?
Replies: 23
Views: 2593

Re: How do you tell a customer...?

The scheme in the link shows 10" (not 10 ohms.) Both in the scheme section and the parts list section. My The Tube Amp Book is 4.1 and I don't see it there.
by jjman
Sat Dec 05, 2015 1:39 pm
Forum: Fender Discussion
Topic: Deluxe Reverb Build
Replies: 15
Views: 3140

Re: Deluxe Reverb Build

At 18ma per OP tube that's probably only about 40-45ma total draw. More draw brings down the voltage somewhat. I run my '71 DR op tubes around 25ma on the plates and the plates are at 440v. (11 watts) If you increase the idle the voltage will come down somewhat. Of course you want to stay within acc...
by jjman
Sat Dec 05, 2015 1:22 pm
Forum: Technical Discussion
Topic: DC on grid of preamp tube
Replies: 4
Views: 1216

Re: DC on grid of preamp tube

DC stabilization on a grid is not optional. Either DC coupling or a grid leak of some sort to ground or bias. I accidentally left one off once and I heard bzzzzzzzzzzzzt thru the speaker. Added it in an there was no damage.
by jjman
Wed Nov 25, 2015 1:20 am
Forum: Technical Discussion
Topic: Debugging some home-made amp problems
Replies: 9
Views: 1255

Re: Debugging some home-made amp problems

Near the top of the pic is a red wire that is black-taped to the chassis. Above the tape it appears to have burnt insulation. No?