Newbie with 6973 amp!

feeds@yuku.com (akimball442) — Sun, 29 Nov 2009 20:33:08 GMT

Hi there-

I am not new to tube amps, but I'm new to this forum.

I have more than a few vintage Fenders, and a 50W Marshall, but I have been getting more and more interested in small amps, which seem to be a lot of fun.
One of my favorites is a small Supro I have, which has only two tubes, a 50L6 and a 12AX7, connected in a power transformerless death arrangement. I figure it's safe enough for the living room.

I recently acquired an old RCA...

Standby lamp shorting?

feeds@yuku.com (jbmojo) — Sat, 21 Nov 2009 10:36:07 GMT

There's a neon standby lamp in my Sound City connected between the two bridge rectifier circuits and I was wondering that if it was shorted would it cause the mains fuse to blow? The bridge circuits are in series for the center tap at the OT and the bulb's connected in parallel with the two B+ outs.
Here's the schematic:

Who uses tube testers?

feeds@yuku.com (DB Electronics) — Wed, 18 Nov 2009 13:39:58 GMT

Does anyone here really use a tube tester. I'm not talking about owning one, just using it on a regular basis.

I sold off all of my tube testers @10 years ago and haven't missed them a bit.
I must admit that by then I was pretty sure I wasn't going to see any tube type televisions any more.

Since then substitution, measurements in known good...

Fender 600 board guide

feeds@yuku.com (jbltwin1) — Fri, 30 Oct 2009 06:12:16 GMT

Anybody here seen a circuit board layout or drill guide for a point to point for the new champion 600? I'm building one for myself and am using an old little pa chassis with it's transformers for a base. The only difference will be that I'll be using a tube rectifier for my supply. Wired it up yesterday for a low end test just to make sure of what voltage I'm getting out of the rectifier and it's right on with 370v with todays power and unloaded. I'm just lazy and...

Scorched PCB ?

feeds@yuku.com (retrorod) — Thu, 29 Oct 2009 06:18:28 GMT

Hi, I am attempting to fix an amp module board for a Rhodes electric piano. It is the 80 watt suitcase model. A resistor next to the transformer flamed up and scorched/charred an area about the size of a quarter. It burnt through the outer layer of the board exposing some of the 'honeycomb' interior of the board. That part is 'dime-size'. I have cleaned up as well as I can. The question is...after I rebuild the traces on the back and install new parts can I expect more...

12AX7 vs. 12AY7

feeds@yuku.com (fredg) — Sat, 24 Oct 2009 15:49:55 GMT

I'm wondering if I can drop the gain on 1/2 of a 12AX7 to get it to around the gain of a 12AY7 (having, let's say, 100K plate resistor, 820 Cathode R ) by messing with cathode resistor alone?

I'm in a situation where I have one socket and I'd like to have 1/2 12AX7 in one half and a "simulated" 12AY7 in the other half (i.e, an extra gain stage driving a 12AY7-type Tweed first preamp tube) - all by using one 12AX7. Is it do-able?

Thanks!

Hiwatt 50w. Hylight Electronics - Early 80s

feeds@yuku.com (SG123) — Tue, 20 Oct 2009 19:15:49 GMT

My friend has one of these, and a 100w. as well from the same era [ that one's signed by Harry Joyce ].
This is the two input, printed circuit version - and they are not the easiest to work on.

It has the large filter cans inside the chassis. I replaced those a few years ago, but the Bright Volume pot finally bit the dust. Of course it's soldered directly to a separate PC board with the rest of the pots and preamp components at the front - solder joints underneath....

Ultra-linear Output Design

feeds@yuku.com (jbmojo) — Thu, 08 Oct 2009 20:18:44 GMT

Are there any undersirable characteristics to be found with ultra-linear amps that anyone knows of? From what I read on Aikin's site they look pretty good for bass or keyboards. Real low distortion, flat response, high output, etc.

fender champ PT ...help!

feeds@yuku.com (bud) — Thu, 01 Oct 2009 18:04:35 GMT

Hey, guys!
I'm new here, and while I've built a few amps with reasonable success, I'm no electronics genius...
I could use a little help.

I'm building a copy of a tweed Fender Champ (5F1) and bought a Weber PT.
The high voltage windings on the secondary side has taps for 600V and 660V, 100mA.
What's the difference?

Also, the primary has taps for 120VAC & 125VAC.
Typical wall voltage in my area can exceed 120V, so I'm...

Filter cap on Ampeg

feeds@yuku.com (vibroworld) — Fri, 25 Sep 2009 22:49:53 GMT

Hi
I am rejuvenating a '61 Reverberocket in New Zealand.
The original schematic only shows 3x20uf filter caps, but this changed shortly after to 6x20uf (which the amp now has, rather crudely strapped onto the side of the chassis)
Either-I go back to 3x20uf as per original and see how much hum is present
or
Sub in a 40x20x20x20 can plus another 20x20 can.
The question is, will the 40uf (commonly available multi section config) adversely stiffen up the supply?...

Tone stack Q

feeds@yuku.com (fredg) — Tue, 22 Sep 2009 22:33:26 GMT

Ok, here comes a question from somebody who really should know better

I have modded a Bandmaster into a '59 Bassman/Marshall JCM 800 single channel configuration. For the most part, I went with the JCM800 component values, with some variation in the tone stack. The tone stack has a 56k slope resistor, 500 pF treble cap, and .022 caps for mid and bass resistors. I have stayed with 6L6 output tubes.

I need to shed some "apparent" bass. The tone stack...

Princeton 6G2 layout

feeds@yuku.com (retrorod) — Sun, 20 Sep 2009 07:52:13 GMT

Hey, I'm in the process of re-building the 'boogered' Prince that I talked about on the Fender amp thread. I am loading the new fibreboard and want to know about the jumper wires from 'A' points. In pics of the '62 chassis it shows the jumpers over top of the components....http://www.flickr.com/pho.../sets/72157620705318112/ Is there any harm in running them under the...

Tech Site

feeds@yuku.com (jbmojo) — Sat, 12 Sep 2009 23:17:50 GMT

Anybody ever been to this site before?
http://mysite.du.edu/~jcalvert/index.htm

It's got a lotta technical info about a wide range of subjects. I ran across it when I googled "vacuum tube data" and thought it might be helpful to some of the young 'uns looking for tech info.

tube/OT impedence question

feeds@yuku.com (jbmojo) — Thu, 10 Sep 2009 20:59:28 GMT

What is the relationship between the output tube impedance(?) and the output transformer? How do you match one up with the other since the plate voltage seems to determine what the tube's' plate resistance is? I'm trying to understand how all the parts in an amp are supposed to interact with each other, so I'm starting at the speaker and working backwards up the line.

using a Morley ABY pedal...

feeds@yuku.com (altercreed5150) — Mon, 07 Sep 2009 18:55:48 GMT

okay, i have a mesa boogie lonestar head with matching 2x12 cab and i have a Bugera 6260. i want to run both heads through the one 2x12 cab...and i have an ABY switching pedal hooked to the inputs of my amps and i only use one guitar...my question is that will it hurt anything if i split the input in the back of the cabinet to use both amps through the one cab? both amps have 8 ohm outputs to the cab which is wired 8 ohms...will the two amps backfeed through the one input signal and hurt...

Ampeg PT

feeds@yuku.com (vibroworld) — Fri, 04 Sep 2009 19:55:43 GMT

Hi
Anyone able to point me to PT specs for a '61 R12R Reverberocket? I need to get a 240V primary wound but normal searches and schematics don't list the secondaries.
Any help much appreciated
Cheers
Vino

Bassman through bass cab?

feeds@yuku.com (burdrock) — Mon, 24 Aug 2009 18:31:17 GMT

hi I'm looking to hook my '68 Bassman head (50 watt, 4 ohm) to a 4x10 bass cab rated 350 watts at 8 ohms. Am I likely to blow anything up with this setup? I'll be plugging a moog synth into the Bassman

Dropping diode question.

feeds@yuku.com (spoony) — Wed, 12 Aug 2009 12:37:22 GMT

I have an ESR amp that I tried a dropping diode to lower the voltage the amp sees 500+. It runs 6l6s and has solid state for the rectifier and preamp. When I used the diode it dropped the voltage everywhere and the amp went cold. So I removed it and have been playing it with the high voltage. It sounds a little farty to me kind of too dynamic if you get what I mean. I was wondering if the high voltages had something...

Minute Man Electronics

feeds@yuku.com (jbltwin1) — Wed, 12 Aug 2009 12:27:03 GMT

Anybody ever dealt with them? I normally get stuff from mouser, allied, parts express, etc., but they have a couple of small things that I need that I have NEVER found anywhere else, AND they have a relatively small minimum order. Just looking for a little feedback. Mike.

PCB edge connectors

feeds@yuku.com (MadDave12) — Thu, 30 Jul 2009 14:48:47 GMT

For a special purpose project (sorry, I've said too much already), I'm sorely tempted to utilize traditional PCB edge connectors for some sub-assemblies within an amp, including all wires running to my preamp tubes.

Any thoughts on the problems I'll see with this approach? I'll watch the distance between bare traces to avoid arcing, of course.

Tech Bench