Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rake on October 15, 2024, 08:48:08 pm

Title: How would this boost work???
Post by: rake on October 15, 2024, 08:48:08 pm: I always thought losing a cathode bypass cap would negatively effect the signal.
This is from the Bedrock Royale Reverb schematic. (Second gain stage)
Title: Re: How would this boost work???
Post by: stratomaster on October 15, 2024, 09:11:42 pm: That will work as a boost. I prefer to short across a higher value resistor (33k-100k, 1/4w) instead of just closing the switch. Less of a pop that way.
Title: Re: How would this boost work???
Post by: kagliostro on October 16, 2024, 12:35:31 am: More readable
Title: Re: How would this boost work???
Post by: Merlin on October 16, 2024, 05:45:44 am: Quote from: rake on October 15, 2024, 08:48:08 pm
I always thought losing a cathode bypass cap would negatively effect the signal.
Losing the bypass cap causes a gain reduction. Therefore adding the cap back causes a gain boost.
Title: Re: How would this boost work???
Post by: SEL49 on October 16, 2024, 07:03:35 am: You can also make the gain adjustable.

https://sluckeyamps.com/smoky/smoky.pdf
Title: Re: How would this boost work???
Post by: rake on October 16, 2024, 08:16:38 am: Quote from: Merlin on October 16, 2024, 05:45:44 am

Losing the bypass cap causes a gain reduction. Therefore adding the cap back causes a gain boost.

So, "normal operation" would be with the boost switch open and boost is when the switch is closed?
Title: Re: How would this boost work???
Post by: Merlin on October 16, 2024, 08:28:35 am: Quote from: rake on October 16, 2024, 08:16:38 am
So, "normal operation" would be with the boost switch open and boost is when the switch is closed?
Yes
Title: Re: How would this boost work???
Post by: rake on October 16, 2024, 12:49:14 pm: Thanks Merlin. For some reason my brain was in bass ackwards mode and couldn't see it the other way around! LOL! :BangHead: :dontknow: :l2:
Title: Re: How would this boost work???
Post by: shooter on October 16, 2024, 01:12:19 pm: Quote
Losing the bypass cap causes a gain reduction.

seem to recall it also "narrows" bandwidth, lower frequencies "fall off" ?
Title: Re: How would this boost work???
Post by: HotBluePlates on October 16, 2024, 01:20:50 pm: Quote from: Merlin on October 16, 2024, 05:45:44 am
Losing the bypass cap causes a gain reduction. ...
Quote from: shooter on October 16, 2024, 01:12:19 pm
seem to recall it also "narrows" bandwidth, lower frequencies "fall off" ?

Not really, because there's no frequency-dependent element to the local negative feedback.

Adding a "small" cap would boost gain for highs, while adding a "big" cap would boost gain for lower frequencies, too.
Title: Re: How would this boost work???
Post by: acheld on October 16, 2024, 09:51:56 pm: Go to https://ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/ (https://ampbooks.com/mobile/amplifier-calculators/cathode-capacitor/calculator/) and you can easily see how size affects frequency response and signal strength.