Search found 13184 matches
- Fri May 03, 2024 12:14 pm
- Forum: Dumble Discussion
- Topic: Transformer transplant
- Replies: 25
- Views: 574
Re: Transformer transplant
Another common source of noise/hum is the loop jacks. If the switching contacts are dirty, you will get hum in the speaker. A good way to test for that is to put a patch cord across the send-return jacks.
- Fri May 03, 2024 11:44 am
- Forum: Garage Talk
- Topic: You guys seen this - Tube making
- Replies: 5
- Views: 120
Re: You guys seen this - Tube making
Same person made a working CRT from scratch too.
- Fri May 03, 2024 10:46 am
- Forum: Dumble Discussion
- Topic: Transformer transplant
- Replies: 25
- Views: 574
Re: Transformer transplant
Just tried lifting the resistor and cap leads and run a wire to the speaker ground as you suggested. That actually made the hum worse; back to more or less the same level as when the OD section of the preamp ground was connected to the speaker/OT ground. Not sure why that would be, maybe some other...
- Fri May 03, 2024 3:50 am
- Forum: Dumble Discussion
- Topic: Transformer transplant
- Replies: 25
- Views: 574
Re: Transformer transplant
There is one part of the above experiment that won’t be optimum, and that is the phase inverter ground, at the junction of the 390 ohm resistor and 2.2 uF cap. That belongs to the power amp, and should be grounded where the OT secondary common is grounded. The short under-board jumper tying that eye...
- Thu May 02, 2024 6:45 pm
- Forum: Dumble Discussion
- Topic: Transformer transplant
- Replies: 25
- Views: 574
Re: Transformer transplant
Shields are the outer braid on the coaxial cables going to and from that pot. I think you can try this as an experiment. Disconnect the wire at the red X, and add a jumper on the main board as shown by the red arch. This seems to be the least invasive way to test the theory. Once you do that, you ca...
- Thu May 02, 2024 4:45 pm
- Forum: Dumble Discussion
- Topic: My take on a 2nd Gen ODS
- Replies: 38
- Views: 1390
Re: My take on a 2nd Gen ODS
Flipping the slide switch layout it looks ok to me.
- Thu May 02, 2024 4:31 pm
- Forum: Dumble Discussion
- Topic: Transformer transplant
- Replies: 25
- Views: 574
Re: Transformer transplant
Yea, not a good idea. I'd ground the shields and the OD trim pot at the input ground eyelet at the center of the board near the 220k. That's probably why grounding the speaker/OT common at the front of the chassis worked well.
- Thu May 02, 2024 3:48 pm
- Forum: Dumble Discussion
- Topic: Transformer transplant
- Replies: 25
- Views: 574
Re: Transformer transplant
Can you post that whole C-tone diagram?
- Thu May 02, 2024 3:46 pm
- Forum: Dumble Discussion
- Topic: Transformer transplant
- Replies: 25
- Views: 574
Re: Transformer transplant
On the snip you posted above, there is an "OD trim pot" connected to the OT common ground. I assume that is the OD entrance trimmer, and I suspect that is the reason it is so sensitive. I would separate that and ground it with the preamp grounds.
- Thu May 02, 2024 1:39 pm
- Forum: Technical Discussion
- Topic: Can I use 6v6's in a 69 Super Reverb ?
- Replies: 15
- Views: 342
Re: Can I use 6v6's in a 69 Super Reverb ?
You are correct! ~12V higher at 200 mA.
- Thu May 02, 2024 1:22 pm
- Forum: Dumble Discussion
- Topic: Transformer transplant
- Replies: 25
- Views: 574
Re: Transformer transplant
The ripple measures around 2,4 Vac before the choke, and around 0,2 V after the choke. I think that is good? So I concluded that the B+ line is probably noise-free. Note that the ripple voltage on the B+ is 100 Hz due to the full-wave rectification. It's nice to check that, but you could have shift...
- Thu May 02, 2024 12:51 pm
- Forum: Dumble Discussion
- Topic: My take on a 2nd Gen ODS
- Replies: 38
- Views: 1390
Re: My take on a 2nd Gen ODS
Wired up the power supply today to do a preliminary smoke check before proceeding any further... Powered it up slowly with my variac and current limiter. No smoke, pops, or blown fuses. B+ values were around what I would expect for an unloaded amp running through a current limiter. Nicely done. So,...
- Thu May 02, 2024 11:12 am
- Forum: Technical Discussion
- Topic: Can I use 6v6's in a 69 Super Reverb ?
- Replies: 15
- Views: 342
Re: Can I use 6v6's in a 69 Super Reverb ?
JJ 6V6S could probably take the voltage. Need to disconnect two of the four speakers to increase the load to 8k. Would that not result in a 4ohms load ? Or am I refering to something different here ? Yes 4 ohms load and 8k impedance on the OT primary for the 6V6S. Maybe swap in a 5Y3 or 5R4 with th...
- Wed May 01, 2024 9:56 pm
- Forum: Technical Discussion
- Topic: Can I use 6v6's in a 69 Super Reverb ?
- Replies: 15
- Views: 342
Re: Can I use 6v6's in a 69 Super Reverb ?
JJ 6V6S could probably take the voltage. Need to disconnect two of the four speakers to increase the load to 8k.
- Wed May 01, 2024 9:00 pm
- Forum: Technical Discussion
- Topic: Can I use 6v6's in a 69 Super Reverb ?
- Replies: 15
- Views: 342
Re: Can I use 6v6's in a 69 Super Reverb ?
The AB568 schematic shows 465V with a very lossy 5U4GB, so the voltage is a bit too high for 6V6, and it will be even higher with the reduced current draw.